Overshadowing the rush of construction to get light rail up and running through downtown Tempe by the end of 2008 is a proposal to extend the train tracks south along Rural Road toward Southern Avenue in the year 2015.

But that proposed two-mile “stub” faces so many engineering and financial problems that history someday could remember it as “the train tracks to nowhere.”

In fact, a study expected to begin in late July could put an end to talk of extending the light-rail system southward toward the Kyrene Corridor.

Instead, south Tempe and west Chandler residents could be offered a steady stream of modern buses along Rural Road and other routes that connect to the light-rail lines.

“The north-south light-rail extension has significant challenges to overcome,” acknowledged Jyme Sue McLaren, Tempe’s deputy public works manager in the Light Rail Transit Division.

But, she added:

“There’s an opportunity in the Rural Road corridor for enhanced transit with BRT (bus rapid transit) and possibly some capital improvements such as a dedicated bus lane, upgraded vehicles, and (traffic) signal priority.”

When local governments put together a light-rail proposal to voters as part of the Proposition 400 half-cent sales tax extension in 2004, Tempe included the two-mile “Tempe South” extension to be built by 2015.

Planning and design for the stub line were to begin this year.

The so-called “Tempe South Alternatives Analysis” study is expected to take until 2009 to complete, but even a layperson can appreciate some of the “significant challenges” that McLaren sees in extending light rail southward on Rural Road.

First is an engineering challenge of crossing the existing Union Pacific railroad tracks near Broadway Road.

McLaren said it is unlikely the light-rail tracks could cross the railroad tracks at grade, so the light rail line would have to bridge the railroad tracks well above street level.

That could involve raising the light-rail line above street level for up to one mile of the proposed two-mile stub line, significantly increasing construction costs and disrupting the Rural Road landscape.

Raising the light-rail line to bridge the railroad tracks also would likely limit the places along the short, two-mile route where passengers could get on or off the light-rail cars.

There also is the question of whether Rural Road, one of the area’s busiest streets, would lose traffic lanes to accommodate light-rail lines, as other area streets have.

Another design challenge would be what to do with a Rural Road light-rail line once it reaches Southern Avenue.

Ending the line at Southern Avenue likely would limit its usefulness, although McLaren noted it would serve the Tempe Library-Senior Center-Museum complex at the southwest corner of Rural and Southern.

Extending it farther south would mean bridging the Superstition Freeway – another expensive engineering challenge, McLaren noted.

Yet another challenge would be deciding whether the Rural Road light-rail stub would have separate cars, requiring passengers to switch trains to continue into Phoenix, or whether to split light-rail service in downtown Tempe, sending some trains south on Rural Road and others east into Mesa, reducing the frequency of service for passengers on both side of the split, McLaren said.

But perhaps the biggest challenge would be to persuade the federal government to share the cost of building the Rural Road light-rail line, especially if it extends only two miles and services a limited number of passengers, McLaren said.

The budget for building the Valley’s light-rail system is based heavily on the assumption that the federal government will pay 50 percent of the costs, she noted. Any portion of the light-rail system not granted federal funds would likely be subject to cost-cutting measures.

The proposal to build a stub line south along Rural Road could be a much more difficult “sell” to the federal government than plans to extend the regular light-rail line farther east into Mesa, she said.

McLaren hastens to add that south Tempe residents will not be neglected if the soon-to-begin Tempe South Alternatives Analysis study determines that light-rail is not practical for southern Tempe.

The Prop. 400 plan included a proposal to turn Rural/Scottsdale Road into a Bus Rapid Transit (BRT) route by 2013, with large, modern buses speeding riders to and from light-rail stations, possibly along dedicated bus lanes that could extend from the Loop 202 in west Chandler as far north as Shea Boulevard.

The rapid-transit buses, which would have fewer stops, would supplement a beefed-up schedule of regular buses, which could run as often as every 19 minutes during busy times.

The Prop. 400 Regional Transportation Plan includes new or improved bus service on Rural Road, Chandler Boulevard, Elliot Road, McClintock, Ray Road and Queen Creek Road.

Even if light-rail never extends into southern Tempe, McLaren has hopes there will be some type of commuter rail service available eventually.

The Tempe South Alternatives Analysis study is likely to look into the possibility of running commuter trains on existing Union Pacific Railroad tracks through the Kyrene Corridor.

Running a commuter rail service on those tracks could alleviate some of the anticipated overcrowding on nearby Interstate 10 and Loop 202, she theorized.