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One thing I discovered at last spring’s Virginia DOT conference on land use and transportation, is that DOTs don;t like developed arterials any more than we do.  Laess actually.  All the curb cuts, volume and signalized intersections called for on developed corrodes turns than into congested nightmares, not just during “rush” hours, but also through much of the day and weeks.  Some of the worst, most durable congestion in the US is found in these corridors.  They find peak traffic at lunch hour and on the weekends, too, as everyone who wants to go anywhere has to get in their car and get on the highway.

The problem is that arterials are built with high capacity to move large numbers of vehicles twice a day  to and from work.  New roads and bypasses as deeded and built specifically to food this.  These new arterials will of course induce traffic, as people that were for merely avoiding traveling the old arterial, or avoiding traveling at all, suddenly see less cost in building along the  fresh new road.  Businesses see this meteoric rise in growth and clamor to get building permits for the highway,with all the attendant curb cuts.

And why not?  The size of transportation resources enables the intensity of development passible at a place.  Any new development of a certain size must show that it is willing to build the extra roads necessary to get people to and from their developments, along with the structure and the parking on their property.  Any major mall or employment center is at the nexus of at least tow major transportation corridors, and sometimes more.  The more ways you have to get to a place, the more people you can get to and from that place.  Without those lanes, you cannot develop the site.

It is little wonder than many arterials get crowded up with fast food, mattress, and convenience stores, each with their own driveway.  Every driveway is a warning to through traffic,and a fresh opportunity for a collision.  Traffic reasonably slows down in response to this, causing congestion that would not be there if the arterial was simply a braid of unadorned lanes.  No wonder traffic engineers hate corridor sprawl.

Traffic Engineers, like Urbanists, would prefer that we build in tidy little clusters connected by undeveloped and quick freeways.  The problem is that that development is almost as much a matter of transportation as it is of wealth.  If you don’t have a way for lots of people to get to and from your place, you have no place.  The ideal way to provide lots of people to a a place would hot have lots of people in that place, reflexively.  That is illegal in most of the US however.

Jacob Riis showed America the horror of overcrowding in 1890’s “How the Other Half Lives” and we’ve been fighting valiantly to uncrowd America ever since.  We have just about, almost succeeded in ensuring that no America need be that close to another American ever again.  The second best way to provide to so of people to a place is with a high capacity transportation system.  Such as a flexible road network with a routine process for adding lanes and a large professional body of evidence for adding new corridors.  New corridors that will get soon crowded with traffic and development, as long as the urban market is right.t

So, what would prevent corridor sprawl?  Succinctly, an understanding that transportation determines land use as much assails, water, and economics, and a willingness to bend the hand of transportation.   If an traffic arterial required walking and biking arterials, and the land use mix to support them, then arterials could be an invitation to urbanism, not traffic congestion, from the start.