Traditional vs. Hierarchical street patterns

The "traditional" street pattern

Prior to the 1950's, the street pattern was laid out in a rectangular grid pattern. Signal lights were few, and four-way stop signs even scarcer, decreasing waiting time. Further decreasing waiting time was the fact that stop lights were short and had only two phases (with a greatly reduced cycle time). There were no long, boring and wasteful waits at stop lights. With few exceptions, streets were just two lanes of traffic, and with a single lane of opposing traffic, left turns were easy because there was often a "break" in the opposing traffic flow. There was a choice of many routes to take, making travel interesting and efficient: routes could be varied to suit traffic conditions or to include errands.

Bicyclists could easily vary the route to suit the expertise of the rider, or select for decreased noise and exhaust fumes. Short traffic signals were pedestrian friendly, creating frequent gaps in the traffic for mid-block pedestrian crossings. The pedestrian had only two lanes of traffic to cross, making both intersection and mid-block crossing much easier and safer. The curb radii were short, increasing pedestrian safety.

Traditional vs. Hierarchical

In the hierarchical example (right), pedestrians, bicyclists and auto users desiring to go westward from the residential development (at center of right map) must first have to literally wind their way eastward to leave the development, exiting on the collector (Main. St., Milpitas), then proceed south to the arterial (Montague Expressway) before being able to proceed westward, using the "exressway" to cross the freeway. In contrast, there are many streets to choose from to go in all directions in this traditional pattern (at left) of an older part of San Jose.

The "traditional" system

Stores, restaurants, and entertainment abut the street. They make an interesting environment for all modes. Car users usually parallel park on the street.

Land use is mixed, further reducing trip length and travel time. Walking, including walking portions of transit trips, is most susceptible to trip length as it relates to travel time. Most urban trips prior to 1950s (and today for many traditional cities) were by transit and walking.

Travel time for transit, bicycles, pedestrians and even most automobile trips is lower for a traditional system. While automobile speeds were also much lower than on today's arterials, travel time was less for reasons described below. (Only long distance automobile trips might be faster in a hierarchical system, but not during rush hour.)

The "hierarchical" street pattern.

The streets are categorized into local streets, collectors, arterials (which include expressways) and freeways. Local streets are designed with winding, random and intermittent street patterns. The purpose of this was to discourage cars from traveling on local streets and encourage them to use arterials and freeways. Stop lights end up with longer and longer cycle times the more congested the road. Arterials are "boring", with views typically limited to parking lots and advertising.

If a route becomes blocked, massive congestion results because there are few or no alternate routes with similar capacity. (In contrast, for a "traditional" street pattern, a blocked street meant that the car user, pedestrian, or bicyclist merely had to detour one block, and then proceed on his/her way.)

Freeways divide up the city, with relatively few places to cross. They became "Berlin Walls" for pedestrians.

Pedestrians and bicycles are prevented from traveling on quiet, local streets for all but immediate neighborhood destinations (see illustration). They must make major detours on account of the street pattern. The effect that a detour, designed for the car user, has on pedestrians and transit patrons was never considered by the traffic engineers. A detour designed to take a car user an extra two minutes for choosing to travel on secondary streets is equivalent to a 20-minute detour for pedestrians and transit patrons! This problem could also have been mitigated by placing alleys wherever a street contains an abrupt turn, and at "T" intersections, to permit pedestrians, transit patrons and bicyclists to proceed in their intended direction of travel. This is common in Europe, but was not done here.

Pedestrians and bicyclists are forced to use arterials, which includes expressways. In California, an "expressway" is an arterial that has few intersections (typically 1/5 as many as other arterials), few driveways, and no parked vehicles. These three special attributes provide added safety for both bicyclists and pedestrians. They also enable the expressways to be "express", decreasing the travel time. Yet, expressways have the same speed limits as other arterials (most were county roads before renaming them as "expressways"). In the past, traffic engineers instituted prohibitions on pedestrians and bicycles on expressways, even though state law only allows prohibiting them from freeways. These prohibitions, in combination with the street pattern, produce major disruptions for pedestrian, transit and bicycle travel modes.

The "hierarchical" system

Land use is highly categorized. Most origins and destinations are deliberately kept apart, increasing trip length and travel time.

To get to stores, people have to walk through unfriendly and boring giant parking lots. Parking lots are unfriendly not only to pedestrians and bicyclists, but also to the auto user who parks and then walks through them. Even small stores must locate in shopping centers and use huge parking lots.

Why use a hierarchical system?

Bigness is more efficient for electric power (high voltage is cheaper per power delivered), water supply or sewers (larger pipes cost less per volume carried). For these systems, smallness is required for the end user (low voltage and small pipes). These two factors result in a hierarchy, where big is connected to smaller that is connected to smallest. A hierarchical system is perfect for electric power distribution (a one-to-many system), water supply (also one-to-many) or sewer drainage (a many-to-one system), and other systems of these two types. Urban transportation is different. It is a many-to-many system.

The concept of "bigger is better" was incorrectly borrowed by traffic engineers. It is a self-serving concept, because much more construction and expense is required, and gives large contracts to the traffic engineers and road builders. However, the rewards are tenuous for automobile transportation. The excessive implementation of hierarchy for roads has actually made automobile transportation worse. It has severely worsened the situation for pedestrians, bicyclists and transit, and drastically curtailed use of these modes.


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