The Problem With Designing Streets For Peak Hour Traffic

When engineers make decisions about streets, they tend to emphasize the “peak hour” — the morning and evening rush when traffic is at its most intense. For the most part, city streets are still designed to move motor vehicles during this relatively short period of time, to the detriment of people outside of cars — i.e. the people who live in the neighborhood.

Bill Lindeke at Streets.mn has been thinking over the implications of this approach to street design. He uses an example in Saint Paul, where the county is considering adding a turn lane to reduce rush hour delay:

By making this change, the Ramsey County study projects that the average car will save a few seconds of time stuck in traffic. For example, according to the model the proposed layout would subtract 20 seconds of delay for Northbound cars while adding a 5 seconds to Southbound cars.

The key thing, though, is that these time savings only occur during the peak hour. For the rest of the day, when the “capacity constraint” isn’t constraining much of anything, the impact on drivers would be negligible.

Meanwhile, for the entire day, the intersection would have worse “LOS” [level of service] for everyone else, especially people on foot trying to cross the street. Adding a turn lane, widening the street, or adding a thru lane (which are three of the options) would increase speeds at the intersection at all times of the day and night, eroding safety for neighbors and anyone trying to cross the street.

Read the rest of the story here.