3 ms·
I'm a pretty big fan of Ontario's parclo design (http://en.wikipedia.org/wiki/Parclo http://en.wikipedia.org/wiki/Parclo). The most standard design (called A4
by jarek 16y ago
I'm a pretty big fan of Ontario's parclo design (http://en.wikipedia.org/wiki/Parclo http://en.wikipedia.org/wiki/Parclo).
The most standard design (called A4 in the wikipedia article) has the same amount of traffic lights as this design. There is no driving on the left, no weaving, and there are no left turns with oncoming traffic.
Access onto the highway is a right turn for all directions. Access from the highway is light-controlled right or left turn. The highway has more capacity than the intersecting road, so while dumping traffic from the road onto the highway at a maximum rate using the easy right turns is fine, the light at the exit off the highway serves as rate limiter if necessary so that the road is not overwhelmed with traffic.
- chancho 16y agoTo be sure, those interchanges are the most pleasant to drive through, but at a cost of land. The interchange design presented in the NPR article is much more feasible in urban centers where you might be constrained by existing structures. The accel/decel ramps can run parallel to the freeway, leading to nearly-right angle turns at street level. (It's not drawn this way in the article, but it doesn't take much imagination to picture it.)
- oozcitak 16y agoDitto on space constraints. Note also that in urban centers existing structures also include underground electricity, water supply, gas, phone lines, etc. which are usually very costly to relocate.
- jarek 16y agoThat's definitely a good point, but in this particular case the picture posted elsewhere in the comments by raquo [1] looks like it could fit or almost-fit a parclo (possibly in a slightly elongated/compressed arrangement). The more hippie side of me is tempted to suggest that if you can't afford the land, you shouldn't be building an expressway there :) [1] http://www.inside-lane.com/wp-content/uploads/2009/11/Diverging-Diamond-Springfield-MO1.jpg http://www.inside-lane.com/wp-content/uploads/2009/11/Diverg...