Old rule of thumb #3: We should require “enough” off-street parking for every use

As Donald Shoup has shown, parking requirements spelled out in zoning codes—often based on formidably inaccurate estimates prepared by the ITE (Institute of Traffic Engineers) lead to a situation where every business’s parking lot is sized for the peak hour of the peak day of the year (holiday shopping season at the Mall, example). Not only does this produce more parking than is needed the rest of the year, it turns out that parking “requirements” grossly overstate demand even in peak periods, and especially for urban uses where more people arrive by other means, and park for shorter periods of time. The product of this rule of thumb is that parking is over-supplied, destinations are further apart than they would otherwise be, and walking, transit and cycling are non –functional.

Old rule of thumb #4: We should plan for a certain number of car trips to be generated by every land use, no matter where it is

Another rule of thumb for planning is that every land use “creates” or generates a certain number of trips. But it isn’t necessarily so: the studies used to make these esimates are drawn from large-scale suburban development where proportionately more trips are by auto. A careful analysis of the data shows that trip generation estimates for most uses are overstated by a factor of 2, leading local governments to require even more transportation capacity than is needed—driving up development costs, and inducing additional travel.

Old rule of thumb #5: We should have a hierarchy of streets

The street hierarchy makes an explicit analogy to the human circulatory system. Just as we have an increasingly fine array of arteries, veins and capillaries, so too does the transportation system have freeways, arterials, collectors and local streets. And we’ve abandoned the traditional street grid for a dendritic pattern. It turns out that these hierarchical street systems are less resilient to disruption and have less capacity than the old-fashioned grids they replace, and are especially hostile to non-automotive modes of travel (pedestrians and bikes are forced to take circuitous routes and are hard to accommodate at the intersections of major arterials that have limited “green” time to accommodate cross=traffic and turning movements. The hierarchal system of “arterials, collectors, and local roads that we’ve adopted in place of the traditional street grid has had the effect of making the average trip between any two points longer. Over the past two decades the “circuity” of trips has increased by 3.7 percent in the nation’s 50 largest metropolitan areas. This increase is on top of the increase in trip distance due to sprawl and decentralization.