All who have commented on how little wear and tear bikes (and for that matter, pedestrians) do.
While strictly true that bikes do little damage, not all road maintenance is needed as a result of traffic breaking down the surface or damaging the structure of the pavement. Dedicated bike ways / multi use trails need regular maintenance the same as roads.
Examples of routine maintenance that would accrue no matter what the traffic load include weather induced damage, such as freeze thaw cycles breaking up pavement, falling trees both directly blocking the route and up turned root balls ripping holes, land slides (happens often enough here in the hilly and wet PNW) and the like. Additionally, there's normal debris removal / sweeping - ever see the roads after a good wind storm? Yeah, again, here in the PNW they're liberally sprinkled with branches and other debris (at least in my area they are - probably less so in down town Seattle). Bike ways / multi use trails here (like the Burke Gilman that runs from the Ballard neighborhood of Seattle to the UW, then north around Lake Washington where it turns into the Sammamish River Trail and goes to Marymoor Park - check the Wikipedia entry for info) would soon over grow if the brush / brambles / sticker bushes on either side in many places weren't cut back on a regular basis. Drainage must be maintained on a regular basis else the road bed will be undermined and fail, or a land slide induced due to over saturation, creek crossing would wash away, etc. Bridges must be inspected on a regular basis for structural integrity and repairs made as needed (from corrosion or the myriad other environmental causes, or just regular protective painting). In snow prone areas, would the dedicated bike / pedestrian routes need to be plowed and de-iced, or left for natural melting / clearing? Roots growing under the paving need to be periodically removed and the paving restored to a even grade (it sure sucks to hit a root caused swell in the pavement on a skinny high pressure tired road bike, doesn't it?).
It would be interesting to know how much is spent maintaining the 27 miles of the Burke Gillman / Sammamish River Trail per annum. As it gets zero vehicle traffic, this would be a good data point on what it would cost (in the PNW at least) to maintain dedicated bike / pedestrian ways.
The point being, that you just can't build bike ways or multi use trails (no matter the funding source) and walk away from them expecting them to be maintenance free since "bikes don't damage pavement". These dedicated routes have to be kept up no matter how "light" the traffic is as the pavement wear and tear is but one aspect of road / bike way / multi use trail maintenance.
