More riders are expected to hop the Purple Line mass-transit project than previously thought, a rep for the state’s transit administration announced.

The fresh numbers, revealed to Silver Spring’s citizens advisory board Monday night, add up to 20,000 trips to guesstimates released in December.

“Our ridership numbers compare very well with other projects,” said Mike Madden, project manager for the transit administration. “We have a good shot — a cost-effective project and one that’s competitive for the limited funds the feds hand out.”

According to Madden, Purple Line ridership could look like this if a bus rapid-transit system is chosen to make the trip from Bethesda, through downtown and east Silver Spring, to New Carrollton:

Bus rapid transit* options Apr ‘08 estimate Dec ‘07 estimate
Low-investment: shared lanes, no tunnels 37K - 40K 29K - 35K
Medium-investment: some shared lanes, no tunnels 49K - 52K 38K - 41K
High-investment: dedicated lanes, some tunnels 56K - 59K 42K - 45K

* “Bus rapid transit (BRT) is a branded bus service that can use standard transit vehicles or advanced technology vehicles, and operates on existing roads and/or exclusive running ways. BRT typically reduces bus travel times, improves service reliability, increases the convenience of users and ultimately increases bus ridership, possibly at a lower construction cost than rail infrastructure.” — Maryland Transit Authority

If the state decides later this year to go with a light-rail system, things could roll like this:

Light-rail transit** options Apr ‘08 estimate Dec ‘07 estimate
Low-investment: shared lanes, no tunnels 57K - 59.5K 38K - 41K
Medium-investment: some shared lanes, no tunnels 60K - 63K 42K - 45K
High-investment: dedicated lanes, some tunnels 65K - 68K 44K - 47K

** “Light-rail transit is an electric railway system that operates single cars or short trains along rights-of-way at ground level, on aerial structures, and in tunnels. Light rail can also operate in the street mixed with vehicular traffic, in the median of a roadway or on a separate right-of-way.” — Maryland Transit Administration

Why the bump? Peg it on passengers who roll mostly on Metro and MARC rail, but who might transfer onto the Purple Line for part of the trip, Madden explained. Those passengers were not included in earlier ridership projections, he said.

Ridership estimates will go through the ringer again in December, when the state decides whether to go with bus rapid transit or light rail, Madden added.

Photo: (lead) An example of bus rapid transit in cloudy Los Angeles. Courtesy of Flickr user LA Wad.