177,000 vehicles per day is a serious traffic volume. According to the map, this is the volume between all exits to Downtown Dallas, so it is through traffic. You can't just detour this traffic via I-35E or I-635. Apart from the required additional mainline capacity, it would also require significant reconstruction of the freeway-to-freeway interchanges, because a typical 1 or 2 lane connector is not designed to handle that kind of additional traffic.
I think they should put the freeway below grade with eight lanes and handle downtown-bound traffic via surface streets, where it can disperse across the grid. A freeway similar to the Woodall Rodgers, but with a longer deck, between 1 and 1.5 mile in length. This will be benificial to both mobility and the city for decades to come.
OK, let's say you have 177,000 vehicles per day. If they are passing through, they don't need to be in the center city. That's why Washington has a beltway, Atlanta has a perimeter, London has an orbital, and Dallas has 635, 161, or LOOP 12 (or lots of other freeways actually). How many does that get rid of?
Then you have people going into downtown. There no reason for anyone with a destination in downtown to need a freeway THROUGH downtown. How many does that get rid of?
Then you have people going from the northern parts of the city to the southern parts. In fact the only remaining people are going from one specific area of Dallas to another specific area of Dallas - because every other direction has a better route. In that instance the remaining motorists, of which there aren't that many, are welcome to use the 22 6-lane and 6 4-lane arterial routes that serve those areas. Ta da.
That's nice in theory. Personally, I think it would have been better if I-45 and I-35E had bypassed Dallas to begin with instead of going through the city center (we'd still need arterial freeways for local traffic, however). In practice, it just doesn't fly, because...
1). 635 can't
remotely handle that traffic. It can't really handle the traffic it has
now. Expanding it to the size it would need to be to handle that much traffic is not at all feasible - the right-of-way issues in some areas (especially the northeast quarter) make it impossible. You'd have to build a completely new outer loop - how much would that cost, and would the through traffic be willing to go
that far out of the way to the east to begin with?
2). Loop 12 certainly can't handle it. The west part of Loop 12 is the only segment which is a freeway; the rest of it is on city streets. There's no really viable connector from I-35E to Loop 12 in the south, much less I-45... you'd have to divert traffic onto I-20 West and then to Spur 408, neither of which is ready for that load... nor is the freeway segment of Loop 12 itself, which already has congestion issues of its own.
3). What "lots of other freeways?". Dallas' freeway and tollway system consists of...
a). Radial routes through the city center - the "spokes" in Dallas' wagon wheel layout:
- I-45 - Part of the main thing you're trying to divert traffic from.
- US 75- The other part of the main thing you're trying to divert traffic from. Really needs to be designated as part of I-45 anyway.
- I-35E - The other thing you're trying to divert traffic from.
- I-30 -West-to-Northeast, also carries traffic into downtown, so it's part of your problem.
- US 80 See I-30.
- US 175 - Routes traffic onto I-45, so it's part of your problem as well.
- Dallas North Tollway - starts in downtown and goes north, therefore not usable for bypassing downtown.
- SH 183 (which I initially forgot), which branches off of I-35E north of downtown and heads northwest, not really relevant to bypassing downtown.
b). Circumferential routes - none of which provides a complete loop freeway
- SH Loop 12 - Previously addressed.
- I-635/I-20 (I still tend to think of this as all being 635, since when I grew up 20 still multiplexed with 30 into downtown) - Previously addressed.
- President George Bush Turnpike - Not even a half-circle at this point, from I-30 to I-30. Certainly not of any use in relieving traffic from I-45 or I-35E, since you can't really get to it from south of downtown without going through downtown!
c). Connectors
- I-345 - 'nuff said.
- SH Spur 366 (Woodall Rogers Freeway) - connector on the north side of downtown, connects I-35E to US 75 and I-345. As it exists entirely in the downtown area, not really relevant to the idea of diverting traffic away from downtown. Also pretty congested already.
- SH Spur 408 - connects I-20 in the south to Loop 12. Previously touched on when addressing Loop 12.
The "other freeways" you seem to think should be handling this traffic do not exist. They would have to be built; while that's a great idea, and might be the best long-term solution for Dallas' traffic problems, where's the money going to come from? And what about the people who live in the areas where those freeways would be built? They wouldn't be any happier about that than Deep Ellum residents are about I-345. Finally, what's going to happen during the time between tearing down I-345 and building the new freeways? It'd make downtown a bigger traffic nightmare than it already is.
In the end, Dallas' freeway system is
designed to route traffic through downtown. Unless you first change
that, removing I-345 would be nothing short of a disaster.
EDIT: Fixed wonky formatting, added SH 183 which I initially forgot.[/list]