Local Airport Access:
From SLAC to SFO: The SLAC to SFO drive route also includes a convenient slip-off from 380 just just before the airport to El Camino then along San Bruno Avenue where there are many gas stations for car refuel. You can simply continue on San Bruno Avenue to car rental return as shown. I280 traffic is normally quite good so that the 25min time estimate is OK for off peak hours. For rush hours you may need at least 45min to1 hour. However, you need to budget in time for rental car refuel, return and air-train to terminal etc.
Rental cars provide an effective local transportation option favored by many regular SLAC users, which will give you more flexibility, and sharing the rental car between a few people will make this even more cost-effective given the discount rates available to SLAC visitor (described below).
Most major rental car companies have many outlets including all major airports (SFO rental car center has many rental vendors altogether in one central building nearby which is very conveniently reachable by air-train). There is a Discount Rental Car Program with Enterprise associated with SLAC which can be used by SLAC visitors, although still worth search for other deals as they can sometimes do better. The Enterprise deal also applies to renting at e.g. Stanford Oaks outlet near SLAC. You should check your institutional travel rental insurance policy. If you have similar policy like Stanford covering both basic and collision damage waiver then you don't need any additional insurance. In case you do need adding insurance, you should ask at the rental desk at airport pickup. There is also the Stanford Zipcar option for very short period rentals.
Other Ground Transportation:
The shuttle system (see list below) has been probably the most popular means of transportation between SLAC/Stanford and airport for travelers until the emergence of Uber and Lyft. Commercial shuttle cost one way ~$30, while regular cabs can be ~$80. However, you need to reserve in advance and allow some extra time for the shared commercial shuttles which may need to do pickups/drop-offs on the way. There has been more regular use of Uber / Lyft by SLAC travelers these days and your dedicated uberX ride between SFO-SLAC has a competitive fare of $38-50 and can call a ride any time without reservation. Uber/Lyft are not allowed to pick up passengers at lower arrival level of SFO so that you need to go up to departure level upstaris to meet your driver there.
CalTrains cannot directly reach SLAC, but can be a useful option for trips to SFO or downttown San Francisco (but need to transfer to BART system at Millbrae), for those staying in downtown Palo Alto, Menlo Park and Redwood City hotels close to a CalTrain station. Palo Alto CalTrain is also a major hub for Stanford Marguerite shuttle system (see below). From CalTrain Station to SLAC is not walking distance. Uber/Taxi may be more viable options when out of Marguerite shuttle operation hours.
Local Transportation around Stanford:
Marguerite Shuttle (Free shuttle around Stanford) has a SLAC Line with stops at the Guest House and between Kavli and ROB inside SLAC. For those staying at hotels just out of the Marguerite shuttle service area, the Santa Clara Transit VTA bus system serves along El Camino Real with line 22 passing in front of Stanford. From Palo Alto CalTrain station you need to take lines N/O or X/Y for change to/from SLAC line at Central campus. From California Avenue, Line SE meets SLAC Line near Governer's Corner. Due to the exchange and many stops, you need to check schedule cacrefully to see how long the whol trip takes. The SLAC Line has limited capacity so that this is not meant to carry the bulk of participants for a major meeting at SLAC. The complimentary Stanford Guest House shuttle is also available evenings and weekends when the Marguerite is not.