I am installing a permeable driveway (Unilock Turfstone) at my house in Portland. I read your article on best types of grass mixes in Oregon. But what about driveway grass? Ideally I would like a grass with low maintenance, less mowing, and for daily parking with car traffic. The driveway is in southeast corner of house and gets full sun, except when parked on in evenings.
Turfgrass well adapted to the Portland area include 1) perennial ryegrass, 2) bentgrass (colonial and creeping), and 3) fine fecuse (creeping red and chewings). Regarding your particular situation, a permeable driveway, I think a traffic tolerant grass species or a species that recovers quickly from traffic are the best options.
1) Perennial ryegrass: The most traffic tolerant grass species of the three options listed above is perennial ryegrass; however, perennial ryegrass will not recover from traffic, it does not produce lateral growth. Luckily perennial ryegrass will germinate in 7 to 10 days and seed is readily available.
2) Bentgrass: Colonial or creeping bentgrass on the other hand, recovers quickly from traffic with lateral growth, but the density will be easily reduced by traffic (more specifically bentgrass will recover from traffic, but has a poor traffic tolerance). This is why sports fields are perennial ryegrass and not bentgrass.
Regarding maintenance levels both, perennial ryegrass and bentgrass will require frequent mowing. Ryegrass will need about 4 fertilizer applications annually (applied at 1 lb N per 1,000 sq ft per application), while bentgrass will need 2 applications annually (again at 1 lb N per 1,000 sq ft per application).
3) Fine fescue: will require the least frequent mowing, fertilization, irrigation etc., but it will not tolerate traffic or recover from traffic.
Considering these limitations I would use 1) perennial ryegrass and interseed when density begins to decrease. Apply seed at 9 lbs per 1,000 sq ft, applying seed at rates higher than this will not improve establishment, but in fact will weaken the turf stand by limiting resources (soil nutrients and water).