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Discussion Starter · #1 · (Edited)
What cities have the best and worst road networks to deal with traffic
congestion? So much focus is given to a cities freeway network when this
question is asked but does a robust arterial network help alleviate the
traffic congestion in a city? The chart below tries to account for the
arterial streets within a city and what effect they may have on traffic
congestion (the chart also includes current INRIX congestion rankings).

A 5-mile radius circle was drawn around the center of each
metro region. The total number of freeway lanes and major arterial lanes
crossing into the city center were counted (little sub-streets crossing into
the city weren't counted). Each arterial lane was counted as half of a lane
to give the total weighted number of lanes for each metro...for example LA
has 157 arterial lanes and 47 freeway lanes entering into the 5-mile radius,
total weighted lanes = (157/2) +47 =125.5.

The Metro population / Lanes entering downtown attempts to determine
how much capacity each lane of traffic would need to carry if every single
person living in the metro area was attempting to enter into the city
center. The cities with the lowest population / lane would potentially be
the cities with the least traffic congestion.

A couple of observations:
Riverside has one of the highest population / lane ratio but has the best
INRIX congestion ranking. May be due to Riverside acting more of a suburb
to LA then acting as a completely separate metro.

San Fransisco has the most limited access into its downtown core with
only 36 arterial lanes and 14 freeway lanes crossing into the city.

Houston & Dallas both have a large number of freeway lanes entering into
its downtown core. Also surprised by the sheer number of large 6-lane
roads and boulevards crossing into downtown.

Atlanta has the highest percentage of freeway lanes entering into the
downtown core. 30% of the lanes crossing into the city are by freeway.
Also, many of the 75 arterial lanes crossing into the city are 2-lane winding

Phoenix has the most rigid arterial street network with very defined mile by
mile blocks. Detroit also has a rigid network of arterial streets especially in
the suburbs. There are several major arterial roads that are wide, straight,
and spoke out from downtown Detroit (Woodward is a straight shot
connecting Downtown Detroit to Pontiac for instance).

Attached some of spotila's great urban density maps for most of the 15 largest
metro regions to get a feel for the cities layout and how the densities may
impact traffic flow (not listed are NYC, Phoenix, Seattle, and Boston).

Los Angeles, CA
City Population: 3,792,621
Metro Population: 17,786,419 (CSA, includes Long Beach, Riverside)

Chicago-Milwaukee Conurbation

Milwaukee Metro Population: 1,751,316
Chicago Metro Population: 9,804,845
Conurbation Population: ~11,600,000

Dallas-Fortworth Metroplex, TX
Dallas City Population: 1,197,816
Fort Worth City Population: 741,206
CSA Population: 6,805,275

Baltimore–Washington CSA, DC-MD-VA
Baltimore City Population: 620,961
Washington D.C. Population: 601,723
CSA Population: 8,924,087

Miami–Fort Lauderdale–Pompano Beach, FL
Miami City Population: 399,457
Fort Lauderdale City Population: 165,521
MSA Population: 5,564,635

Atlanta, GA
City Population: 420,003
Metro Population: 5,268,860

Philadelphia, PA
City Population: 1,526,006
Delaware Valley MSA Population: 5,826,742

Detroit-Ann Arbor-Flint CSA, MI
Detroit City Population: 713,777
Flint City Population: 102,434
Ann Arbor City Population: 113,934
Detroit-Ann Arbor-Flint CSA Population: 5,218,852
Detroit-Windsor Area Population: ~5,700,000

San Francisco Bay Area, CA
San Francisco City Population: 805,235
San Jose City Population: 945,942
Oakland City Population: 390,724
Bay Area Population: ~7,150,000

17,882 Posts
Riverside's downtown is a suburban node like many others in the LA area. Not many people work there. It's also on a population "tendril" rather than the middle of a big area. So maybe it makes sense that there's less capacity heading in and out, even though it's very car-oriented.

I'm a little surprised Seattle ranks so poorly. But then I realize that because of our lakes, canals, and hills, particularly at the five-mile point, a high percentage of traffic narrows down to the types of roads they count. And Downtown is both a big job center and a funnel for the whole region. We ought to have less freeway than we do, but the numbers kind of make sense.
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