Jacobs 1982.

Methods	Design: Controlled before‐after study. Three intervention groups (two treatment arms) and one control group. Duration of follow‐up: 30 days
Participants	Country: USA Setting: University Intervention groups: number of participants not reported. Number of available parking spaces in intervention parking lots were: lot A n=130, lot B n=580, lot C n=186. Control group: number of participants not reported. Number of available parking spaces in control parking lot (lot D) was n=102. Age, gender not reported.
Interventions	Interventions were delivered at the level of the parking lot. Lot A: Drivers entering this lot received a flier with carpooling information. Car occupants were also matched with other potential carpoolers. Reserved parking was provided for carpoolers in this parking lot. A 25c coupon was provided to each occupant each time they parked in the reserved parking for carpoolers (days 10‐28 only) Lot B: Drivers entering this lot received a flier with carpooling information. Car occupants were also matched with other potential carpoolers. Reserved parking was provided for carpoolers in this parking lot. A 25c coupon was provided to each occupant each time they parked in the reserved parking for carpoolers (days 10‐39) Lot C: Drivers entering this lot received a flier with carpooling information. Car occupants were also matched with other potential carpoolers. Drivers were informed that reserved parking for carpoolers was provided in parking lots A and B (but not in this parking lot). Lot D: No intervention. Duration of intervention: 30 days
Outcomes	% of vehicles in car park carpooling each day (with >1 occupant) Effects on inequalities not reported. Adverse effects not reported.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Adequate sequence generation?	High risk	Not randomised
Allocation concealment?	High risk	Not randomised
Blinding? All outcomes	High risk	Not feasible. Could have influenced outcomes
Incomplete outcome data addressed? All outcomes	Low risk	All carparks followed up for full duration
Free of selective reporting?	Unclear risk	Not clear that all pre‐specified outcomes were included
Free of other bias?	High risk	Potential for carpoolers to migrate from lot C to lots A and B not robustly assessed. Could lead to overestimate of carpooling increases in lots A and B.
Adequate matching of intervention / control groups?	High risk	Groups (and their associated parking lots) were of very different sizes and staff:student ratios.