Compendium

Transportation + Highway Engineering — Geometric Design, Pavements, Traffic, Safety

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Transportation + Highway Engineering — Geometric Design, Pavements, Traffic, Safety

Transportation engineering converts mobility demand into the physical + operational infrastructure of roads, streets, intersections, pavements, transit corridors, and active-transport networks. The discipline integrates geometric design (AASHTO Green Book), pavement engineering (AASHTO + MEPDG), traffic engineering (HCM + ITE), safety analysis (HSM), planning (FHWA + MPO methods), and the emerging connected + autonomous + electrified domain. This note covers the technical core + modern updates: AASHTO Policy on Geometric Design 8th ed (2018), HCM 7th ed (2022), HSM (2010 + supplements), MUTCD 11th ed (Dec 2023), FHWA Roundabout Guide + NCHRP 672, Safe System Approach, and the simulation + planning toolchain (Synchro, VISSIM, Aimsun, SUMO).

See also

1. Geometric design — AASHTO Green Book

The Policy on Geometric Design of Highways + Streets (AASHTO; 8th ed 2018) governs US highway geometry. Companion documents: Roadside Design Guide (4th ed 2011 + interim updates), Guide for the Geometric Design of Driveways (2014), Guide for High-Occupancy Vehicle Facilities (2nd ed 2004).

1.1 Design controls

  • Design speed — selected speed by functional class + terrain + access; typical 30–80 mph (50–130 km/h). Posted speed usually ≤ design speed.
  • Design vehicle — controls turning radii + intersection geometry. AASHTO standard vehicles: P (passenger car wheelbase 11 ft), SU-30 (single-unit truck), WB-50 (intermediate semi), WB-62 + WB-67 (interstate semi), WB-67D (double), WB-100T (triple), BUS-40 + CITY-BUS, A-BUS (articulated). Cone of expected vehicles from local truck census.
  • Design hour volume (DHV) — 30th highest hourly volume of the year (K-factor) × AADT. K typical 0.10 rural, 0.08 urban. Directional split D 0.55–0.65 rural.
  • Level of Service (LOS) — A (free flow) through F (forced/breakdown).

1.2 Sight distance

Three categories:

  • SSD (Stopping Sight Distance) = 1.47·V·t + V²/(30·(a/g ± G)). t = 2.5 s perception-reaction time; a = 11.2 ft/s² (3.4 m/s²) deceleration; G = grade. At 50 mph + level: SSD ≈ 425 ft (130 m). At 70 mph: SSD ≈ 730 ft (220 m).
  • PSD (Passing Sight Distance) — two-lane two-way roads only. Eye height 3.5 ft, object height 3.5 ft. AASHTO 2018 tables: PSD = 800 ft at 50 mph, 1500 ft at 65 mph.
  • DSD (Decision Sight Distance) — for complex situations (lane drops, exit ramps, weaving, multi-phase decisions). 1.5–2× SSD typical.

Eye + object heights: AASHTO 2018 eye 3.5 ft, object 2.0 ft (SSD); 3.5 ft eye + 3.5 ft object (PSD).

1.3 Horizontal alignment

  • Circular curves — radius R, degree of curvature D = 5729.6 / R (arc definition) or D = 36000·sin⁻¹(50/R)/π (chord definition).
  • Superelevation e — banking; max e_max varies 4–12 % by snow region + urban/rural. Side friction fs taken from AASHTO Table 3-7 — lower than max-friction tire-pavement to keep comfortable + insensitive to speed variations. Design equation: e + fs = V² / (15·R) (US units, V mph, R ft).
  • Transition (spiral) — gradual increase from infinite to finite radius; clothoid/Euler spiral. Used on freeways + rail. Length per AASHTO formula based on rate of change of lateral acceleration C (~ 1–3 ft/s³).
  • Stopping sight distance on horizontal curves — middle ordinate M = R · (1 − cos(28.65·S/R)), S = SSD along centerline.

1.4 Vertical alignment

  • Grade: max ~ 4 % freeway, 6 % rural arterial, 8 % rural collector, 10 % rural local. Trucks lose speed substantially on grades > 3 % over long stretches; truck climbing lanes added where speed reduction > 10 mph for trucks on grade > 3 % and traffic > 200 vph.
  • Vertical curves — parabolic; defined by K = L/A, where A = algebraic difference in grades (%). Crest curves: K controlled by SSD over crest. Sag curves: K controlled by headlight illumination beyond crest at night (also by drainage + appearance + driver comfort).
  • K-values (SSD basis): for 50 mph, K_crest = 84, K_sag = 96; for 70 mph, K_crest = 247, K_sag = 181 (AASHTO 2018).

1.5 Cross-section

  • Lane width: typical 12 ft (3.6 m) freeway, 11–12 ft arterial, 10–12 ft urban street.
  • Shoulder: 10 ft right + 4 ft left freeway, 4–8 ft arterial. Rumble strips per FHWA SCRSP guidance.
  • Median: divided highways ≥ 4 ft (raised), 30+ ft preferred for cable barrier; 60+ ft for direct median crossing without barrier.
  • Cross-slope: 1.5–2.0 % travel lane, 2–6 % shoulder (matching travel lane on outside of superelevated curves).
  • Roadside clear zone: AASHTO Roadside Design Guide — function of design speed, AADT, side slope. 30 ft at 60 mph, 4.5k AADT, 1V:6H slope.

1.6 Functional classification

FHWA + AASHTO functional system:

  • Principal Arterial (Interstate + Other Freeways + Other Principal Arterials) — long-distance, high-volume.
  • Minor Arterial — intermediate trips.
  • Collector (Major + Minor) — connects local + arterials.
  • Local — direct property access.

Approximately 1.3 M miles principal arterial + minor arterial in US National Highway System (NHS) per FHWA 2024 statistics.

2. Pavement design

2.1 Design methods

  • AASHTO Guide for Design of Pavement Structures 1993 — empirical AASHO Road Test (Ottawa IL 1956–61) based. Still in use by many state DOTs. SN (structural number) for flexible, D (slab thickness) for rigid.
  • AASHTO Pavement ME Design / MEPDG (Mechanistic-Empirical Pavement Design Guide) — released 2008; software AASHTOWare Pavement ME Design v2.6+ (2024). Computes pavement response (stress + strain + deflection) under traffic + climate, then predicts distress (rutting, fatigue cracking, thermal cracking, IRI) via empirical transfer functions.
  • NCHRP 1-37A + 1-40D + 1-47 — research foundations of MEPDG.

MEPDG inputs: hierarchy of Level 1 (project-specific lab data), Level 2 (correlations), Level 3 (default). Outputs: pavement performance over design life (typically 20 + 30 + 40 yr).

2.2 Flexible (asphalt) pavement

Layers: AC surface + intermediate + base + granular base + subbase + subgrade.

Marshall mix design (ASTM D6927) — historical method; 5–7 compactive blows per side; air voids 3–5 %, VMA + VFA criteria. Largely superseded by Superpave (1990s+).

Superpave (Strategic Highway Research Program 1987–1993) — gyratory compaction (75 + 100 + 125 gyrations by traffic level); design air voids 4 %; aggregate gradation control points; binder selection by Performance Grade (PG).

Performance-Graded (PG) binder (AASHTO M 320 + R 28 + R 29):

  • Notation PG XX-YY: XX = high-temp grade (°C; 7-day max pavement temp), YY = low-temp grade (°C; min pavement temp).
  • Common grades: PG 64-22, PG 67-22, PG 70-22, PG 76-22, PG 82-22 (warm + truck-heavy). PG 58-28 + PG 64-28 for cold-region (Minnesota, Maine).
  • Modified binders: SBS (styrene-butadiene-styrene block copolymer; KratonTM, Lyondell), GTR (ground tire rubber), polyphosphoric acid (PPA).

RAP (Reclaimed Asphalt Pavement) — milled old AC. Modern mixes use 15–40 % RAP routinely; 100 % RAP “cold recycled” + central-plant cold-in-place recycling (CIR) common. RAS (Recycled Asphalt Shingles) add 3–5 % stiff binder; less common today.

WMA (Warm Mix Asphalt) — produced at 230–270 °F (110–135 °C) vs HMA ~ 300 °F (150 °C). Lower fume emissions; longer hauling distances; chemical additives (Evotherm, Sasobit wax, Cecabase, MeadWestvaco Synthetic Wax).

2.3 Rigid (concrete) pavement

Three types:

  • JPCP (Jointed Plain Concrete Pavement) — short slabs (~ 12–20 ft) with transverse contraction joints; dowel bars (1.25” diameter epoxy-coated steel) transfer wheel loads. Most common US rigid type.
  • JRCP (Jointed Reinforced Concrete Pavement) — longer slabs (~ 30–100 ft) with longitudinal + transverse steel reinforcement to control crack widths. Largely abandoned 1990s+ owing to mid-slab crack performance issues.
  • CRCP (Continuously Reinforced Concrete Pavement) — heavy longitudinal steel (~ 0.7 % by area), no transverse contraction joints; small-width transverse cracks at ~ 3–6 ft spacing distribute strain. Long-life pavement; common in Illinois + Texas + Belgium. ~ 40-yr design life (3× JPCP).

Concrete mixtures: ASTM C150 Type I/II Portland cement; w/cm 0.40–0.45; air entrainment 5–7 % for freeze-thaw regions; SCMs (fly ash 15–25 %, slag 25–50 %, silica fume 5–10 %); fc’ 4000–5000 psi (27–35 MPa); flexural strength 600–700 psi (4.1–4.8 MPa) controls slab design.

Dowels: 1.25 in diameter × 18 in length, 12 in o.c. transverse joints. Tiebars: #5 epoxy-coated, 30 in length, longitudinal joints.

2.4 Subgrade + base course

  • Subgrade: compacted to 95 % standard Proctor (AASHTO M 145 + T 99 / ASTM D698). Resilient modulus Mr (AASHTO T 307) is MEPDG input; correlations to CBR available but lab Mr preferred for major projects.
  • Subbase: granular A-1 or treated (lime, cement, fly ash, asphalt) for weak subgrades. Provides drainage + frost protection + working platform.
  • Base course: dense-graded aggregate (DGAB; ASTM D2940), asphalt-treated base (ATB), cement-treated base (CTB), open-graded drainage layer (OGDL) for water removal.

2.5 Pavement preservation

Treatments by condition:

  • Crack sealing — hot-poured rubberized asphalt (ASTM D6690 Types I–IV); life 3–5 yr.
  • Chip seal (single + double surface treatment) — emulsion + cover aggregate. Life 5–7 yr. Common rural workhorse.
  • Microsurfacing — polymer-modified emulsion + aggregate + cement; thin (3/8–1/2 in). Used on freeways + airfields.
  • Slurry seal — similar to microsurfacing; lower-stress applications.
  • Thin overlay — 0.75–1.5 in dense-graded HMA. Most common preservation.
  • Mill + thin overlay (mill-and-fill) — restores cross-section.
  • Hot in-place recycling (HIR) + cold in-place recycling (CIR) — full-depth or partial-depth rehabilitation.

FHWA Pavement Preservation Program promotes “right treatment, right road, right time” — preservation costs 10–20 % of reconstruction over a 30-yr cycle.

3. Traffic engineering

3.1 HCM 7th ed (2022)

Highway Capacity Manual published by TRB; foundational reference for capacity + LOS analysis. 7th edition (2022) major changes from 6th (2016):

  • Updated freeway facility analysis with new managed-lane procedures.
  • Connected + automated vehicle (CAV) sensitivity analyses appended.
  • Refined urban-street + signalized intersection procedures.
  • Updated multi-modal LOS (auto + bike + ped + transit) on urban streets.

LOS A through F by facility type:

  • Freeway basic segment: A–E based on density (pc/mi/ln); F when demand > capacity.
  • Signalized intersection: A–F by average control delay per vehicle (≤ 10 s LOS A; > 80 s LOS F).
  • Roundabout: density-based (similar to two-way stop).

3.2 Capacity

  • Freeway basic segment: 2400 pc/h/ln @ free-flow speed (FFS) of 75 mph; varies with FFS, lane width, lateral clearance, ramp density, heavy-vehicle percentage.
  • Signalized intersection: saturation flow rate base 1900 vphgpl (per green hour per lane), adjusted by lane width + grade + parking + buses + area type + lane utilization + left + right turns + ped/bike conflicts.
  • Stop-controlled: gap-acceptance theory; major-street headway distribution + minor-street critical + follow-up gaps.

3.3 Traffic signals

  • Pre-timed (fixed time) — preset cycle + splits; used at saturated coordinated intersections.
  • Semi-actuated — minor street has detection.
  • Fully actuated — all approaches have detection; phases skip if no demand; gap-out + max-out logic.
  • Coordinated — corridor-wide common cycle length + offsets; bandwidth maximization. Synchro + PASSER + TRANSYT-7F design tools.
  • Adaptive — real-time optimization: SCOOT (Split, Cycle, Offset Optimization Technique; TRL UK), SCATS (Sydney Coordinated Adaptive Traffic System), InSync (Rhythm Engineering/Cubic), QuicTrac, Centracs ATMS.
  • ATSPM (Automated Traffic Signal Performance Measures) — high-resolution event data (Indiana DOT + Utah DOT 2014+); FHWA ATSPM open-source platform.

Signal controllers + cabinets: Econolite Cobalt + ATC + ASC/3 + EOS, Siemens m60 + SEPAC + Concert, Trafficware Cubic ATC + 980 + 2070-2N, McCain ATC eX + 3500, PEEK ATC-1000.

3.4 ITE Trip Generation

Trip Generation Manual 11th edition (2021; ITE) — empirical trip rates by land-use code (LUC). 1700+ LUCs with trip-generation rates by AM peak, PM peak, weekday daily, Saturday, Sunday. Used for site-impact analysis + TIA Traffic Impact Analysis.

Companion: Parking Generation Manual 6th ed (2023).

3.5 Microsimulation

  • Synchro 11 + SimTraffic (Trafficware/Cubic) — most common US signal-timing + small-network sim.
  • PTV Vissim 2024 — German-origin, world-leading microsimulation; lane-changing + car-following calibrated to Wiedemann 74 + 99 models.
  • TSS Aimsun Next 23 — Spanish; multimodal, microsim + mesoscopic + macroscopic in one platform.
  • DLR SUMO (Simulation of Urban MObility) — German Aerospace; open-source; large-scale.
  • Quadstone Paramics — UK; airport + complex urban.
  • TransModeler (Caliper) + CORSIM (FHWA, legacy) + Vissim PTV Vistro for signal optimization.

4. Intersection design

4.1 Signalized + unsignalized

  • MUTCD 11th ed Dec 2023 signal warrants (8 warrants): 8-hr volume, 4-hr volume, peak-hour, ped volume, school crossing, coordinated signal system, crash experience, roadway network.
  • Stop control — multi-way stop, 2-way stop. Right-of-way per state UVC.
  • Yield control — common at low-volume + roundabouts.

4.2 Roundabouts

FHWA Roundabout Informational Guide 2nd ed (FHWA-HRT-10-064; 2010) + NCHRP 672 Roundabouts: An Informational Guide (2010) + state DOT design manuals.

Categories:

  • Mini-roundabout — diameter < 25 m, low-volume.
  • Single-lane — 30–45 m diameter; ~ 20,000–25,000 vpd capacity.
  • Multi-lane — 45–60 m+; up to 50,000+ vpd.
  • Turbo-roundabout — multi-lane with spiral lane arrangement, reduces side-swipe conflicts. Dutch origin (1996).

Geometric controls: inscribed circle diameter, central island, circulatory roadway width, entry width, splitter island, deflection (fastest-path analysis ≤ 30 mph for safety).

Safety: 78–82 % reduction in fatal-injury crashes vs signalized intersection (NCHRP 572). Increased adoption: ~ 9000 US roundabouts as of 2024 vs ~ 4000 in 2014 (Kittelson Roundabout Database).

4.3 Alternative intersections (innovative geometric designs)

  • DDI (Diverging Diamond Interchange) — crossover between bridges + ramps; eliminates left-turn opposition. First US DDI: Springfield MO 2009 (FHWA-HIF-14-049 manual). 130+ US installations by 2024.
  • CFI (Continuous-Flow Intersection / DLT Displaced Left-Turn) — left turns crossed over upstream to eliminate conflict with through movements. FHWA Alternative Intersections + Interchanges manual 2010.
  • RCUT (Restricted Crossing U-Turn / Superstreet / J-turn / Synchronized Street) — minor-street through + left movements eliminated; vehicles turn right + use U-turn downstream. Common rural + suburban arterial. NCDOT pioneer; ~ 300 US installations.
  • MUT (Median U-Turn / Michigan Left) — left turns made by going through + U-turning. Originated Michigan 1960s.
  • Quadrant Roadway + Bowtie + Single-Point Urban Interchange (SPUI).

5. Highway safety

5.1 Highway Safety Manual (HSM)

AASHTO Highway Safety Manual 1st ed (2010) + Supplement (2014). Major sections:

  • Part A: Introduction + Fundamentals.
  • Part B: Roadway Safety Management Process (network screening + diagnosis + countermeasure selection + economic appraisal + prioritization + safety effectiveness evaluation).
  • Part C: Predictive Method — Safety Performance Functions (SPFs) for various facility types (rural 2-lane, rural multilane, urban + suburban arterials, freeways, ramps, intersections). Predicted crashes = SPF × CMFs × calibration factor.
  • Part D: Crash Modification Factors (CMFs) — quantify effect of specific treatments. CMF Clearinghouse (UNC HSRC + FHWA) catalogs 1000s of factors.

HSM 2nd edition under preparation (~ 2027).

5.2 Safe System Approach

Adopted by USDOT 2022 National Roadway Safety Strategy. Five elements: Safer People, Safer Vehicles, Safer Speeds, Safer Roads, Post-Crash Care. Foundational principles: humans make mistakes + are vulnerable; responsibility shared among system designers + users; safety is proactive; redundancy is critical.

Vision Zero — initially Sweden 1997 (Nollvisionen); adopted by NYC 2014, Los Angeles 2015, ~50 US cities. Target: zero traffic fatalities + serious injuries on transportation network.

5.3 NHTSA + IIHS

  • NHTSA NCAP (New Car Assessment Program) — 5-star ratings on frontal + side + rollover crash tests; ratings since 1978; 2025 redesign added pedestrian crash + ADAS evaluations.
  • IIHS (Insurance Institute for Highway Safety) — Top Safety Pick + TSP+ awards; moderate-overlap front + side + small-overlap front + roof crush + head restraint tests; pedestrian + headlight + LATCH ratings. Pickup truck small-overlap added 2020.
  • NHTSA FARS (Fatality Analysis Reporting System) + state crash databases — primary US crash data.

5.4 Crash modification factors (selected)

  • Adding centerline rumble strip on rural 2-lane: CMF ≈ 0.86 head-on + sideswipe-opposite-direction (CMF 0.66 fatal + injury, AASHTO HSM).
  • Converting 2-way stop to roundabout (urban): CMF ≈ 0.21 fatal + injury (NCHRP 572).
  • Adding HAWK pedestrian beacon at marked crosswalk: CMF ≈ 0.31 pedestrian crashes (FHWA-HRT-10-042).
  • Diverging diamond interchange (vs conventional diamond): CMF ≈ 0.67 total crashes (Brewer + Murphy 2018).
  • Adding road diet (4 lanes → 3 lanes + bike lanes): CMF ≈ 0.65 total crashes (FHWA Road Diet Informational Guide 2014).

6. Freeway design

6.1 Mainline

Basic segment design controls: design speed → lane width + cross-slope + median + shoulder + sight distance + horizontal/vertical alignment. ASEM ≥ 12 ft lane + 10 ft right shoulder + 4 ft left shoulder (or 10 ft left shoulder if 4+ lanes per direction).

6.2 Interchanges

  • Diamond — most common; suited to crossroads with low cross-volume.
  • Cloverleaf — fully directional but weaving on outer loops; mostly avoided in new construction.
  • Partial cloverleaf (Parclo) — A2, A4, B2, B4 variants.
  • Trumpet — T-intersection of two freeways.
  • Directional + semi-directional — fully directional ramps + flyovers; high-cost, high-capacity (e.g., I-95/I-695 Baltimore, Spaghetti Junction Atlanta).
  • Single-Point Urban Interchange (SPUI) — left turns meet at single signalized point.
  • Diverging Diamond (DDI) — see §4.3.

6.3 Ramps + auxiliary lanes

  • Entrance + exit ramps — parallel + taper designs. Acceleration + deceleration lengths from AASHTO Tables 10-3 + 10-5.
  • Auxiliary lanes — between consecutive ramps if spacing < ~ 1 mile; provides weaving + lane-change space.
  • Collector-distributor (C-D) roads — separate facility parallel to mainline; collects on-and-off ramp traffic from multiple closely-spaced interchanges (e.g., I-91 Hartford, I-95 NJ Turnpike Newark).

6.4 Weaving — HCM Section 12

Weaving section: segment where two adjacent on/off ramps require lane changes within the same segment. HCM 7th procedure: max weaving length + min weaving length + lane changes per vehicle + LOS by density.

6.5 Managed lanes

  • HOV (High-Occupancy Vehicle) — 2+ or 3+ occupants; barrier-separated or buffer-separated. 4500+ centerline miles in US.
  • HOT (High-Occupancy/Toll) — HOV + single-occupant variable toll (typical $0.50–$15/trip dynamic price). I-394 Minneapolis MnPASS 2005, I-15 San Diego Express Lanes 1996, I-95 Express NoVa 2012, I-66 Inside Beltway peak-pricing 2017.
  • Express toll lanes (ETL) — variable-priced; can be 2-lane (each direction) or single. SR-91 OC, LBJ Express Dallas, Lone Star Lanes Tampa.
  • Reversible lanes — barrier-separated or movable barrier (Quickchange Moveable Barrier System). I-15 Express Salt Lake, I-93 NH HOV.

7. Transportation planning

7.1 4-step travel demand model

Macroscopic regional model:

  1. Trip generation — produced + attracted trips by TAZ (Traffic Analysis Zone); cross-classification or regression.
  2. Trip distribution — gravity model with friction factor (deterrence function).
  3. Mode choice — multinomial logit utility model; auto + transit + walk + bike + carpool.
  4. Trip assignment — user equilibrium (Wardrop 1952) on the road network; transit assignment by best-path or stochastic.

Software: PTV Visum (German; world’s leading regional model platform), TransCAD + Maptitude (Caliper), Cube Voyager (Citilabs/Bentley), VisionEval + Trip Generation in Open Source (TGOS) (open).

7.2 Activity-based models (ABM)

Replaces trip-based 4-step with agent-based simulation of full daily activity patterns. Used by SCAG, SANDAG, ARC, NCTCOG, BMC, PSRC, others. Tools: DaySim (Resource Systems Group), CT-RAMP (Parsons Brinckerhoff), POLARIS (Argonne National Lab open-source), ActivitySim (open-source consortium 2017+).

7.3 MPO + statewide + transit planning

  • MPO (Metropolitan Planning Organization) — federally-designated for urbanized areas > 50,000 pop. 400+ US MPOs. Develop RTP (Regional Transportation Plan, 20+ yr) + TIP (Transportation Improvement Program, 4 yr).
  • State DOT statewide LRTP + STIP.
  • NEPA (National Environmental Policy Act 1969) — EIS Environmental Impact Statement, EA Environmental Assessment, CE Categorical Exclusion. FAST Act 2015 + IIJA 2021 + IRA 2022 funding cycles.
  • NEPA + permitting updates 2023 BUILDER Act + One Federal Decision streamlining.

7.4 Transit planning

  • BRT (Bus Rapid Transit) — dedicated lanes + signal priority + level boarding + off-board fare collection + branded vehicles. ITDP BRT Standard (Gold/Silver/Bronze/Basic). US examples: Cleveland HealthLine, LA Metro Silver Line, Pittsburgh East Busway, NYC SBS Select Bus Service.
  • LRT (Light Rail) — Phoenix Valley Metro (2008+), Charlotte LYNX Blue (2007+), Denver RTD, Minneapolis Hiawatha, LA Metro E + A + L + K Lines.
  • Heavy Rail / Metro — NYC Subway (largest US, 472 stations + 850 mi), DC Metro, BART, Boston MBTA, Chicago CTA, MARTA, MIA, Honolulu Skyline (2023+).
  • Commuter Rail — LIRR, Metro-North, NJ Transit, MBTA Commuter, Metra, SEPTA Regional, Caltrain, Sounder.
  • Streetcar / Tram — Portland Streetcar, Seattle Streetcar, Atlanta Streetcar, Cincinnati Bell Connector, Detroit QLine.

FTA Capital Investment Grants (CIG) — New Starts (≥ $400M, ≥ $150M federal), Small Starts (< $400M, < $150M federal), Core Capacity. Project evaluation: mobility + cost-effectiveness + congestion relief + environment + land use + economic development.

8. Bicycle + pedestrian + complete streets

8.1 Design references

  • AASHTO Guide for the Development of Bicycle Facilities 4th ed (2012; 5th ed under development).
  • NACTO Urban Bikeway Design Guide (2014, ongoing updates) + Urban Street Design Guide (2013) + Don’t Give Up at the Intersection (2019). Increasingly adopted by US cities + endorsed by FHWA.
  • MUTCD 11th ed Dec 2023 — long-awaited update; added bike-signal warrants + new colored-pavement provisions + revised pedestrian signal timing requirements.
  • PROWAG (Public Right-of-Way Accessibility Guidelines) — US Access Board final rule 2023.

8.2 Bikeway typology

  • Class I — Shared-use path — fully separated from motor traffic.
  • Class II — Bike lane — striped lane in roadway.
  • Class III — Bike route — signed only; shared travel lane.
  • Class IV — Separated bike lane / cycle track — physically protected in-roadway. NACTO + AASHTO 2024 supplement. Curb-separated, parking-protected, planter, flex-post protected.
  • Bicycle Boulevard / Neighborhood Greenway — low-volume + low-speed street with traffic calming + wayfinding + arterial-crossing improvements.

8.3 Complete streets

Federal Complete Streets Act incorporated into IIJA 2021. State + local Complete Streets policies (1700+ adopted). Design guidance: Smart Growth America Complete Streets Coalition, ITE Designing Walkable Urban Thoroughfares 2010.

8.4 Pedestrian crossings

  • Marked crosswalks + mid-block crossings + HAWK High-intensity Activated crossWalK / PHB Pedestrian Hybrid Beacon (per MUTCD 11 Section 4F) + RRFB Rectangular Rapid Flash Beacon + LPI Leading Pedestrian Interval (3–7 s head-start before parallel traffic green) + Scramble (Barnes Dance).

9. Connected + Autonomous Vehicles (CAV)

9.1 V2X — Vehicle-to-Everything

  • DSRC (Dedicated Short-Range Communications) — IEEE 802.11p + WAVE protocols (IEEE 1609.x stack), 5.9 GHz band. FCC reduced US allocation to 5.895–5.925 GHz Nov 2020 + reassigned 5.850–5.895 to unlicensed Wi-Fi.
  • C-V2X (Cellular V2X) — 3GPP Release 14 (LTE-V2X) + Release 16+ (NR-V2X 5G New Radio). Direct mode + network mode. Federal preference + most OEM roadmap now C-V2X.
  • BSM (Basic Safety Message) — SAE J2735; ~ 10 Hz broadcast of speed + heading + position + braking; basis of forward-collision warning + intersection-movement-assist + emergency-electronic-brake-light.

USDOT CAMP Cooperative Automotive Research for Advanced Mobility — Crash Avoidance Metrics Partnership, V2X System Engineering, multiple cities deploying.

9.2 SAE J3016 levels of automation

  • L0 — no automation; warning only.
  • L1 — single-function (ACC or LKA).
  • L2 — combined (ACC + LKA; e.g., Tesla AP + Mercedes Drive Pilot urban + GM Super Cruise + Ford BlueCruise).
  • L3 — eyes off, hands off; OEM must respond in limited ODD (Mercedes Drive Pilot 95 mph approved June 2024; Honda Legend; BMW Personal Pilot L3).
  • L4 — fully autonomous in geofenced ODD (Waymo Phoenix + SF + LA + Austin 2024+; Zoox + Cruise — Cruise suspended 2023; Apollo Go China; Pony.ai; Motional).
  • L5 — fully autonomous everywhere (no commercial deployment).

9.3 Roadway sensing + HD mapping

  • LiDAR HD maps — Mobileye REM, TomTom HD Maps, HERE HD Live Map, Argo AI (defunct 2022), DeepMap (Nvidia acquired 2021).
  • Roadside Units (RSU) — Cohda Wireless, Kapsch TrafficCom, Siemens Sitraffic ESCoS.

9.4 Federal + state policy

  • NHTSA AV TEST + AV 4.0 Ensuring American Leadership in AV Technology (2020 + ongoing).
  • 49 CFR 571 FMVSS exemptions for AV deployment.
  • State legislation in 40+ states permitting AV operation; California DMV AV testing permits (Waymo + Cruise revoked Oct 2023 + others).

10. Electrification + charging infrastructure

10.1 EV charging levels

  • Level 1 (L1) — 120 V AC, 1.4–1.9 kW; overnight residential.
  • Level 2 (L2) — 208–240 V AC, 3.3–19.2 kW; workplace + public.
  • DC Fast Charge (DCFC) — 50–350 kW DC; highway corridor. Standards: CCS Combo, CHAdeMO (declining), Tesla NACS / J3400 (adopted as SAE standard 2023; nearly universal OEM adoption 2024–2025).
  • MCS (Megawatt Charging System) — 1+ MW; heavy-duty trucks. CharIN standard; Tesla Semi prototype + Daimler eActros 600 + Volvo VNR Electric 2024+.

10.2 Charging networks

Tesla Supercharger — 50,000+ stalls global (2024); now open to non-Tesla via NACS adapter. Electrify America (VW Dieselgate consent decree, 800+ stations US). EVgo (1000+ DCFC). ChargePoint (200,000+ ports global, largest L2 network). Blink + Tritium + ABB E-mobility + Wallbox + EVBox + Alfen + Allego.

10.3 NEVI Formula Program

National Electric Vehicle Infrastructure Formula Program — IIJA 2021; $5 B over 5 yr to states for DCFC every 50 miles on Alternative Fuel Corridors + interstates. 4 × 150 kW CCS per site; 24/7 access; uptime 97 %+. Buy America requirements (final rule Mar 2024).

10.4 Roadway management

  • TIM (Traffic Incident Management) — FHWA Strategic Highway Safety Plan; Traffic Incident Management Self-Assessment.
  • Variable Speed Limits (VSL) + Queue Warning + Hard Shoulder Running + Active Traffic Management (ATM) — Seattle WSDOT, Minnesota MnDOT MnPass, FHWA Active Transportation + Demand Management.

11. Asset management + pavement performance

11.1 Asset Management Plans (TAMP)

MAP-21 + FAST Act + IIJA require state DOTs to develop risk-based TAMPs for NHS pavement + bridges. Performance targets:

  • Interstate Good ≥ 50 %, Poor ≤ 5 %.
  • Non-Interstate NHS Poor ≤ 10 %.
  • NHS bridge condition: Good ≥ 50 %, Poor ≤ 10 %.

11.2 Pavement condition measurement

  • IRI (International Roughness Index) — m/km or in/mi; smoothness measure. Profilometers: Ames Engineering, ICC SurPRO, Dynatest, Pavemetrics Laser Crack Measurement System (LCMS).
  • PASER + PCI (Pavement Condition Index, ASTM D6433) — visual distress survey.
  • Falling Weight Deflectometer (FWD) — Dynatest 8000 + 9000, JILS, KUAB, Carl Bro PRIMA — measures pavement structural response to dynamic load; backcalculation of layer moduli.
  • Traffic Speed Deflectometer (TSD) — Greenwood Engineering; structural assessment at network speed.

11.3 ARAN + automated condition surveys

  • ARAN (Automatic Road Analyzer) — Fugro Roadware; multi-sensor van captures GPS + IMU + IRI + transverse profile + cracking + rutting + GPR.
  • Pavemetrics LCMS-2 — laser line + camera at highway speed; 3D pavement profile + crack detection.

12. Software + tools (consolidated)

ToolVendorUse
AutoCAD Civil 3DAutodeskRoadway design + drafting
OpenRoads DesignerBentleyRoadway + corridor design
InRoads + GEOPAKBentley (legacy)Older DOT standard
MicroStationBentleyDrafting platform
AASHTOWare Pavement ME DesignAASHTOWareMEPDG pavement design
WinPAS + PerRoad + PaveExpressTXDOT + WAPAPavement design
Synchro 11 + SimTrafficCubic/TrafficwareSignal timing + microsim
PTV Vissim + Vistro + VisumPTV GroupMicrosim + signal + macroscopic
Aimsun NextTSSMulti-scale traffic sim
SUMODLROpen-source microsim
TransCADCaliperTravel demand modeling
HCSMcTrans / Univ FloridaHCM-based analysis
SIDRA IntersectionAkcelikRoundabout + intersection
AutoTURN + Vehicle TrackingTransoft + AutodeskTruck turn-path analysis
IHSDMFHWAInteractive Highway Safety Design Model
CMF ClearinghouseFHWA + UNC HSRCCrash modification factors
NRBI + RNS + AASHTOWare SafetyAASHTOWareSafety analytics

13. Notable projects + corridors

  • US Interstate System — 48,000 mi (77,000 km); construction begin 1956 (Eisenhower-signed FHA), substantially complete 1992 (I-105 LA last new segment); federal cost $129 B 1956 dollars (~ $600 B 2024).
  • Boston Central Artery / Tunnel “Big Dig” — 1991–2007 — $15 B (1991 dollars; ~$24 B with interest); replaced elevated I-93 with 3.5-mi tunnel + extended Ted Williams Tunnel to Logan Airport. Slurry walls + ground freezing in Boston Blue Clay; multiple safety + tile-fall incidents; 1 fatality 2006.
  • I-405 Sepulveda Pass HOT Lanes Los Angeles 2014.
  • Houston Katy Freeway (I-10) widening 2008 — to 26 lanes (general + HOV + frontage); regularly cited as example of induced demand.
  • California High-Speed Rail — partial construction 2015+; Bakersfield-Merced 119 mi segment targeted 2030.
  • Brightline West (Las Vegas–LA HSR) — 218 mi; groundbreaking April 2024; $12 B; expected service 2028.
  • DC + Baltimore Maglev — Northeast Maglev Consortium; SCMaglev Japanese tech; SR + ROD pending 2024+.
  • Eglinton Crosstown LRT Toronto — 19 km; protracted construction 2011–2025+; original $5.3 B → $13 B+.
  • Crossrail / Elizabeth Line London — 73 mi; opened May 2022; £18.9 B; transformed central London capacity 10 %.
  • HS2 (UK High-Speed 2) — 530 km London–Birmingham–Manchester–Leeds; Phase 2 north canceled Oct 2023; Phase 1 (London–Birmingham) under construction targeting 2029–2033.
  • Mumbai Trans Harbour Link opened Jan 2024 — 21.8 km longest sea bridge India.

14. Funding + financing

  • HTF (Highway Trust Fund) — federal fuel tax 18.4 ¢/gal gasoline + 24.4 ¢/gal diesel; unchanged since 1993, declining real revenue + EV erosion. General-fund transfers since 2008.
  • IIJA / BIL 2021 — $1.2 T over 5 yr; $110 B new highway investment.
  • GARVEE bonds + TIFIA loans + PABs (Private Activity Bonds) — federal credit assistance.
  • P3 (Public-Private Partnership) — DBFOM Design-Build-Finance-Operate-Maintain; major US: Capital Beltway HOT Lanes (Transurban + Fluor 2008), I-595 Florida (ACS + Bouygues 2009), I-95 Express VA (Transurban 2014), Indiana Toll Road, Pennsylvania Turnpike Conversion 2007.
  • VMT (Vehicle Miles Traveled) tax — Oregon OReGO program 2015 pilot, Utah, Virginia. Expected to replace fuel tax as EV adoption grows.

15. Emerging issues

  • Equity + Justice40 Initiative — federal mandate that 40 % of certain investments flow to disadvantaged communities (Executive Order 14008, Jan 2021).
  • Resilience + Climate Adaptation — IIJA PROTECT Program; sea-level rise + flooding + extreme heat impacts on pavement + bridges. FHWA Climate Resilience Pilot Program.
  • Urban Mobility + 15-minute cities — Carlos Moreno concept (Paris); land-use + transportation integration.
  • Curb management + micromobility — Bird + Lime + Spin e-scooters; e-bike share (Lyft Citi Bike, Bay Wheels, Capital Bikeshare, Divvy, BIXI Montreal); shift in curb allocation from parking to delivery + loading + bike + scooter parking + outdoor dining + parklets.
  • Climate-Resilient Pavements — high-modulus asphalt; thicker bases; alternative binders + aggregates; CTAG climate-tech advisory group.

Further reading

  • AASHTO Policy on Geometric Design of Highways and Streets 8th ed (2018). The “Green Book”.
  • Transportation Research Board — Highway Capacity Manual 7th ed (2022).
  • AASHTO — Highway Safety Manual 1st ed (2010) + 2014 supplement.
  • AASHTO + ARA Inc — Mechanistic-Empirical Pavement Design Guide: A Manual of Practice 3rd ed (2020).
  • Yang H. Huang — Pavement Analysis and Design 2nd ed (Pearson, 2003).
  • Nicholas J. Garber + Lester A. Hoel — Traffic and Highway Engineering 5th ed (Cengage, 2015).
  • Roger P. Roess + Elena S. Prassas + William R. McShane — Traffic Engineering 4th ed (Pearson, 2010).
  • Carlos F. Daganzo — Fundamentals of Transportation and Traffic Operations (Elsevier, 1997).
  • Donald T. Hartgen + M. Gregory Fields — Gridlock and Growth: Why Cities Have So Much Traffic Congestion (Reason Foundation, 2009).
  • Vukan Vuchic — Urban Transit: Operations, Planning and Economics (Wiley, 2005) + Urban Transit Systems and Technology (Wiley, 2007).

Adjacent

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