In print: Toll autoways, autolanes?

Gary Alstot, prof. engineer, of Laguna Beach California argues for increasing the capacity of some expressways by segregating autos from trucks. In many states the old 12 ft general purpose lanes are being restriped down to 11 ft on urban expressways to squeeze in an extra lane by also taking space from a shoulder or median (4x12’ lanes plus 2x10’ shldrs for example becoming 5x11’ lanes and 2x6.5’ shldrs.) But Alstot argues that a more radical narrowing of lanes should be achieved with autos-only roadways and/or lanes which could be 10 ft wide. For a 5.5’ (66 inch) wide car (about half cars on U.S. roads were this width or less in 1991/92) a 10’ lane would provide the same side clearance as trucks (at 8.5 ft width) get on 12 ft lanes. Alstot argues substantial economies are possible: 16 percent less pavement area and also less stress and damage to pavement structure from the lack of trucks.

Lesser overhead requirements could offer another option: low doubledecking. The classic doubledeck expressway is the I-110 Harbor Freeway just south of downtown Los Angeles. It is one thing to elevate the upper deck above the trucks on the ground level roadways, but when they come to overpasses the upper deck has to soar over those too, lifting the whole structure 50 feet in the air. By adopting parking garage style headroom, Alstot proposes doubledeck passenger car lanes that go under overpasses. See diagram:

Alstot says most freight railroad lines in urban areas are underutilized and thinks that trucks could be run on them — either by paving them for joint use by trucks and trains or with special bimodal vehicles. (“Optimizing the Use of Urban Freeways and Railroads,” Transportation Congress Proceedings, American Society of Civil Engineers, San Diego, Cal., Oct. 1995)