Planning a cohesive system

We had a big question come from Ralph a few weeks ago, and it took a little doing to get a good answer. He asked:
When you expand I-10 or US281 on the North side, why not add at least one more outbound lane than inbound lanes. Outbound lanes function like a "drain" and the faster you get cars out of the city, the less strain you place on the highways that are in the city. Too many inbound lanes can cause overload on the roads in the city so inbound lanes and outbound lanes function differently from a system level. So, add more outbound lanes. You do not need an equal number of inbound and outbound lanes.

To begin, Ralph, we have a major challenge to accommodate the more-than 150 new cars on San Antonio-area roads popping up daily while meeting current needs. Yes, you read that right. We have been adding more than 150 new cars (per the San Antonio Mobility Coalition) to the roadways in the San Antonio metro area alone every single day for the last few years.
There's a bit of a process that goes into determining where to bring major capital improvements and how to address current and future demands. We begin by measuring traffic volumes - as well as projections - for both inbound and outbound directions on our major corridors. Thanks to new technologies we're able to make pretty good determinations regarding the origin and destination of these trips as well.

What we are finding is these volumes (and future projections) are pretty darned equal for both inbound and outbound traffic. That is, just as many people are using those inbound routes as are using outbound routes. The data shows us the strain on surface streets is pretty similar between evening and morning hours.
We take these findings to a determining body responsible for planning a cohesive system - in the case of the San Antonio metro area, we go to the Alamo Area Metropolitan Planning Organization. This group allows us to place our projected development projects in context with future development by city and county governments. In short, the MPO looks at the transportation system as a one-piece body and ensures development by one agency coincides with development with other agencies.

With the needs identified by the MPO, an extensive public involvement process ensues. Armed with the public input and significant data from state and local engineers (and consultants), priorities are determined.
Then we have to identify funding - which is much easier said than done.
The details of the projects are designed during the funding process, and our designs are vetted by you through open house meetings. (Seriously, we do change designs based on public input - it happens all the time.)
With public input we finalize the details of plans and let the project for bids. By rule we offer the contract to the lowest bonded bidder, then approve the contract through the Texas Transportation Commission. It takes about three months to get the contract signed and the contractor ready to go (typically), then we get going on the project.
Whew.

That's the process, Ralph. But to answer your question much more directly, we don't add an additional lane to the outbound traffic because we typically see the same demand on both directions of traffic. One option that might come in to play later on to accomplish what you're suggesting, and as local needs increase, is to use reversible highway lanes ... but that's something folks here simply haven't been ready to implement yet. You may see it used in the future, though - particularly as HOV lanes take shape with more efficiency in the region and mass transit becomes more important to the Alamo City.