Transportation Engineering Expert

---
name: transportation-engineering-expert
version: 1.0.0
description: Expert-level transportation engineering covering highway design, traffic flow, intersection design, pavement design, traffic impact studies, and public transit.
author: luo-kai
tags: [transportation, highway design, traffic flow, pavement, intersections, transit]
---

# Transportation Engineering Expert

## Before Starting
1. Highway design or traffic operations?
2. New facility or existing system analysis?
3. Urban or rural context?

## Core Expertise Areas

### Traffic Flow Theory
Flow, speed, density: q = k times u, fundamental flow relationship.
Greenshields model: linear speed-density relationship, parabolic flow-density.
Capacity: maximum sustained flow rate, varies by facility type.
Level of service: A through F rating of traffic operations quality.
HCM: Highway Capacity Manual, standard methods for capacity and LOS analysis.

### Highway Geometric Design
Horizontal alignment: tangents and circular curves, superelevation.
Stopping sight distance: based on design speed, reaction time, braking distance.
Vertical alignment: grades and crest and sag vertical curves.
Cross section: travel lanes, shoulders, medians, clear zones, slopes.
Design speed: governs all geometric design elements.

### Intersection Design
At-grade intersections: signalized, stop-controlled, yield-controlled.
Signal timing: cycle length, phase splits, offsets for coordination.
Roundabouts: yield at entry, continuous flow, fewer conflict points than signals.
Interchange types: diamond, cloverleaf, directional for grade separation.

### Pavement Design
Flexible pavement: asphalt surface on granular base, AASHTO design method.
Rigid pavement: concrete slab on base, controls deflection and cracking.
ESAL: equivalent single axle load, accounts for different vehicle weights.
Pavement condition: IRI, PCI, distress surveys for maintenance planning.

## Best Practices
- Collect actual traffic counts before designing improvements
- Check sight distance at all critical locations
- Design for design year traffic not just current conditions
- Consider pedestrian and bicycle needs in all transportation design

## Common Pitfalls
| Pitfall | Fix |
|---|---|
| Ignoring pedestrians in signal timing | Include pedestrian crossing time in phase lengths |
| Insufficient sight distance on curves | Check both stopping and passing sight distance |
| Underdesigned pavement for actual trucks | Use actual axle load data for ESAL calculations |
| Wrong LOS method for facility type | Use HCM method specific to facility type |

## Related Skills
- structural-engineering-expert
- hydraulics-expert
- construction-management-expert