Posted: Mon, 16 Aug 2010 03:09 PM - 11,747 Readers

By: Ben Wear

What's Up With That is back from vacation.

Q: I drive South MoPac Boulevard to work, and for the past few weeks it's looked like they're building a sidewalk in the median. But you'd have to cross freeway traffic to get to the sidewalk. What's up with that?

A: Nope, not a sidewalk. It's the concrete base for a "cable barrier" fence being installed in the median, similar to what exists on sections of North MoPac. The cable barriers, although they look flimsy (just a series of posts with steel cable strung between them), are designed to either stop or seriously slow down cars that career out of control and head into the median. They prevent head-on collisions, in other words.

Q: On West Fifth Street near MoPac, they've installed a traffic light at Campbell Street (at El Arroyo restaurant) and turned it on about a week ago. With all those people entering Fifth from MoPac and Lake Austin Boulevard headed downtown, won't a traffic light back up traffic? And why was it needed in the first place?

A: City traffic engineer Ali Mozdbar says all the relatively new development in that area has increased traffic on Campbell, particularly at lunch (there's a sports bar on West Sixth Street as well as the popular El Arroyo on West Fifth) and during the evening commute. And increasingly people park on the south side of West Fifth at the new Gables Residential apartments, he said, and then try to dash across Fifth to get to El Arroyo or other places between Fifth and Sixth.

So he said those pedestrians and the cars on Campbell justified a light. However, the light on Fifth will go red only when a car on Campbell triggers pressure sensors under the pavement, or when a pedestrian presses a button at the crosswalk. A car on Campbell will need only about 10 seconds of green and yellow to get through, Mozdbar said, but a pedestrian will make Fifth Street cars face about 22 seconds of red light.

Given the high speed of cars coming off southbound MoPac to Fifth, Mozdbar said, the city will install a flashing light on the ramp to indicate when the light on Fifth at Campbell has gone red. We'll all see how well this works in practice.

Q: Those crosswalks with blinking lights are confusing. I've seen people sit there on a blinking red light and no one in the crosswalk. What should a driver do?

A:Those crosswalks (there are four in Austin, with two more on the way) have a constant blinking yellow when no one's around, which means proceed with caution. But when a pedestrian presses a button, the lights go to solid yellow, then solid red, then back to blinking red.

The pedestrian is supposed to be out of there by the time the blinking red comes on. If they aren't, of course, wait for them to clear.

But a blinking red is essentially equal to a stop sign, Mozdbar said. So if there's no pedestrian still in the walk, you can drive on after coming to full stop.