The traffic calming effect of narrower lanes is well documented. Vehicle speeds reduce and safety increases as lanes narrow down to about 10.5 feet from the North American standard of 12 feet.
What would this narrowing mean in terms of cost for a typical new urban development? About 10 percent of the surface area for these developments is traffic lanes. This excludes curbside parking, driveways, sidewalks, boulevards, parking lots, etc. So narrowing by 10 percent from 12 feet to 10.8 feet would free up 1 percent of land area. This is nice but we can do a lot better.
If we were to replace most suburban two-lane streets with either one-way streets or lanes and swales the savings would be over 3 percent. In the article, Useful Paving, “Road surface typically accounts for 13 to 15 percent of a subdivision’s total area. What if we could use that 13 to 15 percent better? In our model system, the parkways and main streets could accommodate 80 percent of traffic.”
And if we could replace arterial roads (see widening of the arteries) with old town main streets and through roads, the savings would be another 2 percent.
So now, we have reduced traffic lanes by 50 percent, which means just 5 percent of a typical new urban development is devoted to traffic.
Unfortunately, mobility has dropped as well. Reducing peak speeds from around 35 miles per hour down to around 25 miles per hour reduces mobility by about 30 percent. This is an enormous cost in time and money.
I see two solutions.
The first is to beef up through roads. Increasing the number of through road lanes, and increasing even flow with roundabouts can increase average speeds and reduce peak speeds at the same time.
The second is to introduce a network of transitways. These would provide cross-town mobility at about 40 miles per hour with no intersections.
As architectural cost consultants the total traffic lane reductions for the park city could be calculated as approximately 30 percent, or 3 percent of the total area. Construction Cost would be reduced significantly for through roads by replacing traffic lights and stops signs with roundabouts. The cost of the transitway would be paid for by the 30 percent reduction in paved surface (or 3 percent increase in saleable land area).
Oh, and none of this includes the cost saved by fewer injuries and fatalities.
In an interview on sustainable design, Richard Vermeulen stated that “Even more reduction could occur with lane widths going from 12’ to 10’ or 10.5’. The main reason for super-wide lanes is the requirement for emergency vehicles, namely the Big Old Red Fire Truck . Our current approach of adding lanes to counter the effect of stop-and-go traffic creates Widening of the Arteries . When we eliminate lanes, we can also shrink their width and create Even Flow at reduced speeds with higher volume.” This is illustrated in [PDF] 2061 The Park City – Vermeulen
To find out more, Green at No Cost: Economic and Cost Control Strategies the Create No Cost Sustainability, is available from Amazon.
Richard Vermeulen is co-CEO, lead economist, and chief estimator for Vermeulens. Richard has developed industry-leading standards for estimating and data-basing complex construction projects throughout North America. He is the author of Vermeulens Market Outlook and the Green at No Cost and Save-Save Solutions blog. He is a recognized speaker at national conferences on the topic of construction economics, urban planning, and architectural design.
“The rate of side-impact crashes is lowest on urban streets with lanes about 10.5 feet wide — much narrower than the standard 12 feet. Graph: Dewan Karim”
The “forgiving highway” approach to traffic engineering holds that wider is safer when it comes to street design. After decades of adherence to these standards, American cities are now criss-crossed by streets with 12-foot wide lanes. As Walkable City author Jeff Speck argued in CityLab last year, this is actually terrible for public safety and the pedestrian environment.
A new study reinforces the argument that cities need to reconsider lane widths and redesign streets accordingly.