The Denver Rocky Mountain News presents a more comprehensive look at why FasTracks is going over budget and why RTD may struggle a bit with the burden. The blame is being laid on rising materials costs:
Since FasTracks went up from its original price tag of $4.7 billion to $6.1 billion in May 2007, there has been another year of hefty inflation in the construction industry - fueled by hikes in steel, concrete and oil. The Colorado Construction Cost Index, a measure of costs for transportation projects maintained by the Colorado Department of Transportation, increased 6.1 percent last year.
Unfortunately, this means that Denver's fledgling light rail network is facing some peripheral cuts, but even that doesn't look like enough to keep the costs under control. Narrower bike trails and fewer cameras only buy you so much and then you're looking at cutting much more than the optional landscaping.