You can't blame the communities that will eventually enjoy new rail service from FasTracks for having a wish list about the amenities they'd like to see along the forthcoming lines.

Jefferson County has objected to the plan to reduce the West Corridor from two tracks to one between the Federal Center and the County Government Center in Golden; the line was pared to a single track as a cost-cutting move a few months ago.

Meanwhile, community leaders and other residents along the Northwest Corridor between downtown Denver and Longmont have inquired about electric rather than diesel trains, because electric units are quieter and pollute less.

Neither wish could come true without busting the budget - in the case of electric units to Longmont, by hundreds of millions of dollars. At some point, fiscal reality must prevail. So must the calendar.

For the Regional Transportation District to meet voters' expectations to roll out FasTracks on time and within an ever-tightening budget, some hoped-for niceties just aren't possible. Local leaders should acknowledge as much and let FasTracks move forward.

Jeffco's request is nothing new; officials there have bristled at the notion of a single track from the time it was floated late last year. But eliminating one track will save a bunch of money - $36 million - and RTD's ridership forecasts found that a second track isn't necessary.

Trains can run at intervals of no more than every 15 minutes on a single track, yet that should satisfy anticipated demand.

Jeffco hasn't backed down. It's refusing to sign an agreement with RTD to allow the project to proceed.

The county says the line will attract enough riders to justify 10-minute intervals, meaning the second track would have to be built. Or RTD would need to build an additional "passing" lane to allow additional trains to run.

The passing track would cost $3 million to build.

On Tuesday, the RTD board voted 14-0 to authorize the single-track plan, with or without Jeffco's approval; the district is nearing a deadline to apply for federal transit funding and needs to move forward.

Fortunately, the two sides are still talking. RTD is expected to offer Jeffco an agreement with "triggers" that would let FasTracks add cars to each train and even possibly build the passing track later if ridership exceeds the district's forecasts. Jeffco should accept that deal.

Meantime, some local officials and residents along the Northwest Corridor asked RTD if it was realistic to electrify the lines, which will mostly run in a right-of-way alongside freight trains.

This was more of an inquiry than a demand, and RTD asked the BNSF railroad about the possibility. The answer should give those who'd prefer electric units there sticker shock.

The railroad cited "significantly increased capital \[and] future maintenance costs," including the need to rebuild bridges to accommodate the power lines that would fuel electric units. RTD estimated rebuilding could require between $405 million and $565 million more than is now in the budget.

So electrification isn't a realistic alternative, unless communities along that line can come up with the extra money.

And that's what others who are near FasTracks' footprint should expect from this point forward. Daydreaming is fine, but this region will be fortunate if FasTracks is completed on schedule without cutting too many more corners.