Traffic Travis | RM 620 Congestion Bad, But Maybe Not Enough To Pursue Fixes

AMERICAN-STATESMAN STAFF

LAKEWAY - Dave DeOme has lived in Lakeway eight years, long enough to get elected mayor twice. And long enough to know that traffic on RM 620 is a problem, particularly around Lake Travis High School just before and after the school day, and getting worse.

"The high school puts the highway in tilt mode for about an hour in the morning and an hour in the evening," DeOme said. "You can get traffic backed up for a mile or more. All you need is a little hiccup."

DeOme said Lakeway residents also see the huge Lakeway Regional Medical Center about to open just up the road, and the steady march of other development along RM 620, the main street of western Travis County.

Residents can't help but wonder, he said, if that sporadic school-related jam will soon become an all-the-time part of life in the Lake Travis region.

"And it scares them," DeOme said. "There's no other route, and it's one way out and one way in."

Traffic on the 18.5 miles of RM 620 between Texas 71 in Bee Cave and U.S. 183 in Northwest Austin has more than tripled in some stretches over the past 20 years, ranging in 2010 counts from 26,000 vehicles a day just west of Mansfield Dam to 41,000 a day just south of RM 2222.

Yet despite the rising traffic volume, and continuing population boom in western Travis County, Central Texas' 25-year transportation blueprint contains no plans to widen the five-lane thoroughfare.

Officials say that the traffic, while certainly more troublesome than in the road's more bucolic and relatively recent past, still falls into an acceptable range for a road of that design. And accident rates are below statewide averages for urban ranch-to-market and farm-to-market highways.

Simply put, RM 620 will have to wait its turn.

"When you look at the state's top 100 congestion list, you see what the Austin list looks like, and 620 was not on it," said Carlos Lopez, the Austin district engineer for the Texas Department of Transportation.

Loop 360 (Capital of Texas Highway), for instance, was No. 72 on that list, Lopez said.

The 11-county TxDOT Austin district in 2010 was allotted $543 million for building or expanding roads over the next decade, he said, and that money has already been parceled out to roads with more serious congestion or safety problems such as MoPac Boulevard (Loop 1), U.S. 290 and U.S. 183.

"By the time you try to deal with these very, very high-volume types of roads, $543 million doesn't go very far," Lopez said.

If RM 620 improvements aren't on the horizon, it is due at least in part to expansions that occurred on it many years ago when existing traffic perhaps did not yet justify the investment.

The Texas 71-to-U.S. 183 stretch, with minor exceptions, has had five lanes since 1989 when traffic counts were just 8,000 to 14,000 cars a day.

Since then, new developments, including the 4,600-acre Steiner Ranch master-planned community, have funneled more cars onto the road. From 1990 to 2010, population in census tracts along the road increased from 42,000 to 108,000, a 156 percent increase.

Calculating congestion

Figuring the capacity of a road is not a cut-and-dried matter, given variations in terrain, speed limits and the frequency of traffic lights.

But a TxDOT highway manual for an "urban street" with 40 mph traffic and three traffic signals per mile shows that the road could accommodate about 3,100 vehicles an hour and still get a C grade, well within the acceptable range.

A road or intersection is not considered beyond capacity until it gets to an F grade, which in this urban street example would be somewhere above 3,600 vehicles an hour.

RM 620, however, actually has a 55-mph speed limit and, in this stretch, an average of 1.6 traffic lights per mile, so the actual capacity is somewhat higher than those figures from the TxDOT manual.

Lopez said a traffic rule of thumb is that a highway sees about 10 percent of its vehicles in the peak hour of morning rush and then again at the afternoon commute's worst hour. By that measure - he said actual hourly figures are not available - RM 620 would be seeing 2,600 to 4,100 vehicles an hour at those peak periods, putting it above a critical level only as it nears RM 2222.

Crash statistics, meanwhile, put it between 117 wrecks per 100,000 miles driven (in the stretch between the dam and RM 2222) and 177 wrecks per 100,000 miles (between RM 2222 and U.S. 183).