In the case of 345, that means much of the energy and vitality that would be on the city street grid gets vacuumed up onto the limited access highway. Because of the limited access nature of highways, you have little option to re-route if the highway is already congested, which it invariably is at peak hours.
It's important to understand all of the different types of traffic that end up on 345 competing for the same limited space. As I've outlined before these are 1) long haul freight - which should be re-routed outside the city, 2) long trip commutes - say 15 miles and up, which we'll get into, and 3) short trip commutes which shouldn't be on a highway to begin with.
Using the handy dandy mapping tool from the census that tracks origins, destinations, and commuting patterns I wanted to get a better look at where South Dallas commuters were actually going and how far they were going. Further, we tend to treat origins and destinations as gospel and something that must be catered to when in fact they are the product of current infrastructure and are incredibly malleable.
Basically, the bigger and faster you make infrastructure the further people end up traveling because the further apart destinations became. You stretch out the tax base while larding up tax burden for that heavy infrastructure. It's incredibly costly to spread apart destinations on both the public sector and private sector. Effectively, distance between things is an extra tax to participate in the local economy.
Furthermore, while we confuse highways as convenient or as mobility, it's also worth noting these are only the case when everything must be accessed by car. That also means only those of driving means, age, and ability can take advantage of that subsidy. We're subsidizing those that can afford driving the most while punishing those that can afford driving the least, or those that can't drive at all.
The first map above shows the top 50 job destinations by census tract for the entire southern sector, ie everything south of I-30 within Dallas County. You'll see that a whopping 6% of all jobs for those that live in this huge area are in the very large census tract that incorporates the hospital district (UTSW, Parkland, Children's, etc). Interestingly, very few of the top 50 census tracts for jobs are east of 45/75 corridor. Oddly, Travis County is the third highest job center.
Next I'm zooming in just on SE Dallas County, the area between the Trinity around to I-30 including Pleasant Grove, Seagoville, Balch Springs, Mesquite, and South Dallas. Again, most of these jobs are in the hospital district and extend up the 35 corridor from downtown to 635. Other than 35 the jobs also cluster along 635.
I wanted to zoom in a bit more on the downtown and hospital district map because for these jobs it is worth noting that 345 is never the most convenient route to reach these according to google maps. It's either to take 45 to 30 to 35 through the downtown mixmaster (and who wants to do that?) or exit 45 to Cesar Chavez to Pearl to Harry Hines. The city streets. However, I'm guessing many take 345 despite the inevitable backups on Woodall Rodgers and 345 because it seems like it 'should' be faster.
The above graphic shows where all the jobs are for SE Dallas County where people are commuting 10-24 miles to reach. The software segments commuting length into the following dimensional categories: 0-10, 10-24, 25-50, and over 50 (like woah). I selected 10-24 because this is the most common distance for SE Dallas commuters, accounting for 46% of total jobs.
Above is all commutes from SE Dallas County. The question we should be asking is why must this area commute to the opposite end of the county for jobs? And, why are 68.6% of commutes over 10 miles? We should be able to re-create many of these jobs 1) closer to downtown and South Dallas. By re-orienting downtown as the center of job growth, rather than up and down 75 and 35 the by-directional traffic between jobs and homes isn't competing for the same space. In other words, South Dallas and North Dallas shouldn't ALL be commuting on 75. But it is.
Above is a zoom in on those jobs under a 10 mile commute. The two hotspots are Mesquite and downtown Dallas.
Above is all of the jobs people are commuting from SE Dallas between 25 and 50 miles to reach. They're mostly west or northwest
Lastly, are the jobs people are commuting over 50 miles to reach. These are in Austin and to a lesser extent, Waco.
So who would actually use 345 that should?
Looking at the top 10 zip codes for jobs of those living in SE Dallas County, none of them are up 75 until you reach 635. Every time I've input commutes emanating from SE Dallas/Pleasant Grove to Richardson and points north 635 is always the recommended route not 345/75.
If we're assuming that 345 makes the most sense for the jobs south of 635 but north of Woodall Rodgers, that's only 3 zip codes of the top 25. The are as follows:
Zip code Jobs % of Total Jobs
75206 1733 1.2%
75081 1634 1.2%
75204 1449 1.0%
75204 is the uptown/cityplace area, which could be reached easily with a conversion to a grid. Even so, that's a total of 3.4% of the SE Dallas County resident job commutes that would find 345 convenient.
First, we should be bringing more jobs closer to SE Dallas by removing the highway. Second, we shouldn't let 3.4% prevent bringing those jobs closer because they're dependent upon a section of road where the dirt beneath is now worth far more to the real estate market (and its ability to supply affordable housing and job creation) than the cost of maintaining that infrastructure.