It is the position of FAR that due to the "wilderness" and nonresidential nature of the (unofficial) Alewife bike path that any artificial surface should be of a pervious nature. A pervious surface will allow natural water flow into the ground and prevent water erosion except in very heavy rains while providing a surface more conducive to biking and skating. This surface should be durable enough to resist cracking due to heavy vehicles (DCR maintenance trucks), be relatively low maintenance and, as much as possible, resist root damage from neighboring trees.

A brief survey of pervious surfaces:

Kara Construction - http://www.perviouspavement.com/default.html
This Florida company builds concrete based porous surfaces. Concrete based surfaces have the advantage of not being asphalt based and therefore not susceptible to oil leaching. Concrete also has the natural property of becoming stronger from continued exposure to water. It doesn't address frost heave resistance (since it is FL based). I have inquired for more information from them on pervious concrete.

Georgia Concrete & Products Association - http://www.gcpa.org/pervious_concrete_pavement.htm
This Georgia manufacturers association has useful details on concrete based pervious surfacing. It touches on flow rate (up to 3-5 gallons per minute per some area it doesn't identify), lower freeze-thaw damage due to small void spaces, and clogging (washing restores 80-90% of capacity).

Greenbuilder.com - http://www.greenbuilder.com/sourcebook/PerviousMaterials.html
This builder's information site mentions some considerations for roadbeds. Pervious roadbeds may require a clay substrate if vehicles are expected on it but consideration for using the most porous subbase as possible must be taken to prevent water pooling. Soil compaction during building also needs to be avoided. Pervious surfaces can cost 10-40% more than a regular asphalt surface.

Washington Aggregates & Concrete Association
- http://www.washingtonconcrete.org/industry/pervious/pervious_pavement.shtml This concrete industry site mentions that trails will need about 4 inches of surface. It also mentions that freeze/thaw is not an issue as long as the water can pass through and away from the surface.

Rock Products
- http://rockproducts.com/mag/rock_pavements_leak/ This aggregate trade magazine site mentioned that freeze/thaw damage will only occur if a rapid freeze occurs when the concrete or asphalt is still soaked (and thus ice forming in the voids). It says asphalt based pervious surfacing has been used in cold areas but there isn't much data on it's performance. It feels though that the bigger voids in asphalt would cause it to break down faster than concrete.

Conclusion:

• Crushed rock makes a decent bike surface but can turn muddy when wet (personal experience) and will erode over time. The current bike path surface resembles finely crushed rock and sandy soil.
• Asphalt can leach oils over time, which should be avoided in a wetlands area.
• Pervious concrete surfaces have an established performance history and can survive cold weather.
• The bed is very important and needs to be pervious also to drain water away from the surface as fast as possible.
• The surface should only expect very infrequent vehicle traffic and so can be made to trail specifications (about 4 inches thick of surfacing).
• Expect to pay ~10-40% for pervious surfacing more than for plain asphalt.
• Some pervious surfaces allow for grass to grow on it or between sections. This would be fine for bikes but would prevent skating.
• The surface needs to be low maintenance. Pervious concrete's small voids and restorability via simple washing give it a plus here. Maintenance would still need to be yearly, mainly to wash it off, remove debris, and cut back vegetation to prevent root cracking.
• Most pervious concrete usage has been in warm weather or mild winter states such as CA, FL, TN, VA, WA, OR.

Based on all of the information it seems pervious concrete laid on a pervious bed (sand or crushed rock) is the best option. This surface provides the best balance between price, rideability, durability, and water porosity. The appropriate organization should plan on washing off the surface at least once a year and keeping vegetation back a few feet from the edges.

Other resources:

NJ Stormwater Best Management Practices Manual - Standard for Pervious Paving Systems - http://www.njstormwater.org/tier_A/pdf/NJ_SWBMP_9.7.pdf
This site is a very good source of information but from a roadways perspective. The information is still applicable but from a smaller perspective.

Concrete Bike Ride - http://www.concretebikeride.com/
This group is organized by concrete manufacturers and others to promote and build concrete based bike paths. It is based in Virginia and provides grants to concrete bike path builders (and has done so in at least 6 states).

Betterroads.com - http://www.betterroads.com/articles/aug03a.htm
General pervious concrete info.

Concrete Network - http://www.concretenetwork.com/pervious/
Pervious concrete promotion but has good info and links to usage, etc.

http://www.greenresourcecenter.org/MaterialSheetsWord/PermeablePaving.pdf
A nonpartisan group with info on permeable surfaces