In the United States, the national 'Commuter Choice' program allows employers to re-imburse employees for commuting expenses up to $100/month as a tax-deductible expense for the employer and a tax-exempt benefit for the employee. To qualify as a vanpool, the vehicle must be used 80% for commuting to work, must seat 7 people (including the driver), and must be used with at least 4 occupants (including the driver) on average. The driver is eligible for $175/month parking fees in addition to the monthly commuting expense.
This incentive program allows employers to provide a valuable benefit to their employees tax-free for both the employee and the employer.
These tax benefits are in addition to the natural benefits of carpooling including shared daily fuel and toll expenses and use of HOV lanes.
These links provide more information about the government incentive programs:
US Commuter Choice program.
US State incentive programs.
American Public Transportation Association
Carpoolworld.com is the best way to find commuter matches for ridesharing in your community.