Project Summary
When buses and cars are mixed together in a city’s (limited) street infrastructure, they interfere with each other and create or exacerbate congestion. These cross-modal (bus-car) interferences, and the flow disruptions thus created, are particularly severe because the two modes are physically very different and have very different performance characteristics in terms of speeds, accelerations, maneuverability, etc. Thus for a given number of person trips, the mixing together of buses and cars creates more emissions than if each mode were to operate within its separate right-of-way.
In recognition of the above, transportation engineers and planners have attempted to separate the modes, for example by creating BUS Rapid Transit (BRT) corridors. While a BRT strategy can be useful in some settings, it has an important limitation for most cities in California: BRT corridors require short headways (between consecutive bus arrivals) along a route of no more than about 1 minute, so as not to waste the road space taken away from the other modes. Consequently, BRT should be focused on only a few select corridors in California.
Our plan is to develop dynamic strategies to share road space so that buses can be segregated from cars when bus headways are large. In this way, the strategies could enjoy wide-scale deployment and blanket cities throughout California. We will explore the use of bus lanes that activate and deactivate intermittently. These intermittent lanes would essentially function as a set of rolling cocoons, with each cocoon starting at the rear bumper of its bus and extending some distance ahead. The latter zone is kept clear of non-bus traffic to prevent bus delays. For practical reasons, this exclusion zone might advance discretely one street block (or freeway link) at a time. Variable message signs, possibly combined with lane lights on the pavement and other communication technologies, would announce changes to drivers. Although the presence of these intermittent lanes reduces capacities and creates delays for non-bus traffic, our preliminary analysis indicates that these impacts can be far less severe than what occurs when a travel lane is permanently dedicated to buses.
We note that this Dynamic Infrastructure Sharing (DIS) would be especially helpful for advancing California’s High Speed Rail, since its success will require superb multimodal access to High Speed Rail stations.