Central Business Districts, Functionally Unified

​

What does it mean for a central business district to be unified, not split-in-two? Today, Manhattan's office centers are split into Downtown, Midtown, and Midtown South. 

​

From observing existing business districts, traffic data, and talent agglomerations, business districts lose their functional unity in both specializations and commuting patterns when there is more than a 5 minute difference from its first freeway exit to its last freeway exit (same for subways----from the first station to the last). Because subway trains need to stop frequently, 5 minutes in Manhattan will move commuters little over one mile. Business districts which try to spread themselves further quickly split in two.

​​

On the other hand, a consistently 120 mile-per-hour freeway enabled by autonomous mobility could produce a business district ten miles long by ten miles wide, or one hundred square miles. Defining autonomous freeway speeds will be important for defining how large downtowns could be.

​

How Fast Can autonomous Freeways Go?

​

There may be practical limits with freeway speeds as they begin to supersede 100 miles-per-hour with variables like the wind and even mild bumps in the road surface beginning to cause hard-to-manage jumps in jerk and acceleration above one meter-per-second-squared (the industry standard used for mass transit), making rides uncomfortable. Faster freeway speeds may also require excessive energy consumption compared to air planes, not to mention longer reaction times that could conversely require a decrease in traffic flow compared to a slower freeway with quicker reaction times. These may be some of the reasons that futurists dating back to the 1930s dreamed of freeways with top speeds of120 miles-per-hour. If cities prepare for the possibility of 120 mile-per-hour freeways and plan out a metropolitan region by spacing out future travel times, 120 mile-per-hour freeways may still be the best assumption we have.

​

Limiting Factors

​

A downtown freeway can only have so many off and on-ramps before growing functionally too crowded for merging. Exit routes can only travel so far from the main freeway before they become time-inconvenient. Exit routes must be crossable for pedestrians and local traffic, lowering each exit's flow potential.

 

These are powerful limiting factors. My metro area-wide prioritization algorithm systemically targets exit routes to not exceed half of their capacity during peak traffic to handle the moment-by-moment variance of arriving traffic for each freeway ramp. In needed, variable pricing of traffic could relieve connected traffic systems from relying on selective congestion. All of these factors create limits for what a highest-volume managed autonomous traffic routes can look like.

 

Currently, human drivers are unable to coordinate merging, which gives freeways diminishing marginal returns in traffic processing which rarely justify building more than five lanes for each direction, as extra lanes create more traffic for the extra merging. By contrast, computer-guided traffic could enable near-perfect merging and allow freeways to carry more freeway lanes, so long as there is enough right-of-way committed for merging at strategic points, whether for personal vehicles or mini-buses. Merging patterns could be important for the rights-of-way cities need to secure for automated traffic. All of Autonomous Symmetry's designs are predicated on merging equations.

​​