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The topology of transportation modes is important as to how they are going to be used, and the how well our transportation network fits with their needs.

A good way to think of this might be to use a theoretical arterial and looking at how commuters might using walking, biking, traffic, or transit travel along this arterial in their commute.  Even though the commute is not the majority of the miles or trips that we take, it is the travel most of us notice the most.  Our roads, and transit are sized for the peak use during that commute.  Even though the commute peak use happens a couple of hours a day, we have to deal with its artifacts around the clock.

Starting with the median and modal distances for commutes in 2009, consider a dozen commuters living in the same neighborhood with a nearby arterial.  What routes would they take?

For traffic, the arterial connects to a network of other arterials, which offer unsurpassed choices of destinations.

For transit, passengers using transit are not going to use transit unless it gets near where they want to go.  Their destinations will hew to the arterial more faithfully than any other mode.  Sufficiently wide arterials endanger transit passengers in their return journeys.  Crossing six lanes of traffic to get to a transit stop can be dangerous, especially with left and right turns, especially after dark.


For walking and biking the arterial is more of an obstacle than a conduit.  The traffic arterials, with high speed vehicles or blockades or inattentive, harried commuters, lined by curb cutes to expanses of parking with destinations behind.  Walkers and bikers get the signal, and their routes only use the arterial where they have to.


Of course, walk and bike trips have to take the route network that is available to them.  If the scale of the blocks is not walkable or bikable, people will walk or bike less.