How Are Arterial Roadways Engineered for Heavy Traffic?

Arterial roadway engineering is the civil design of high-capacity urban and suburban streets: the pavement structure, the horizontal and vertical geometry, the drainage, the access management, and the intersection and signal design that make the corridor function. The design balances mobility against access. An arterial that provides too much driveway access stops moving traffic; one that provides too little strangles the businesses along it. The engineering is in finding the balance the corridor's land use demands.

The pavement structure is the most expensive element per mile and the one the public judges. The design starts with the subgrade — tested, not assumed — and builds up through base and surface courses sized for the traffic loading. Drainage is part of the pavement design, because water in the base destroys pavements faster than traffic does. I insist on real geotechnical data for arterial pavements. Default subgrade values are how under-designed pavements happen, and the cost of the borings is trivial compared to a premature reconstruction. The pavement section is a 20-year decision made on day one.

Arterials have to work on opening day and in year twenty. My review covers the structure, the geometry, and the operations. Here's the checklist.

• Pavement section is designed for projected truck loadings on tested subgrade values
• Geometry meets the design speed: sight distance, curves, and grades
• Access management plan controls driveway spacing and turning movements
• Drainage design keeps water off the pavement and out of the base
• Intersections are designed for the turning movements with appropriate signal or roundabout control
• Pedestrian and bicycle facilities are integrated, not squeezed in afterward