Marooned in a sea of swiftly overheating cars, Mark Snider was enduring yet another Cape Cod traffic snarl one hot August afternoon in 1980. The cause of the tie-up was a lengthy freight train laboring through a highway crossing. But rather than swear at the offending freight, Snider found himself smiling. Inspiration had struck.

Today Snider, 26, presides over the Cape Cod & Hyannis Railroad, which chugged into operation the summer after that traffic jam on the strength of a $55,000 loan from a company owned by his father, a resort developer. Rolling along 46 miles of existing track between Hyannis and Falmouth, the railroad has ferried more than 80,000 passengers and grossed roughly $1.5 million this year. Running between April and November, the CC&H offers a variety of junkets, from the $19.75 train/boat combo to Martha's Vineyard to the $5 Sunset Special that scoots along the coastline.

Nicknamed "Sparky" by his staff, Snider spent the winter of 1980-81 lining up equipment, setting up stations and finding skilled crews. His engine is a silver Alco diesel from 1947 and his favorite find is a 1912 parlor car bought at auction for $23,000. As president of CC&H, Snider is paying himself a modest $20,000 for 1983, the first year his railroad has been in the black.

Snider's interest in transportation dates to his childhood in Chestnut Hill, Mass. and a basement train set. Summers in Nantucket fostered a fascination with the sea as well. During his school vacations he worked as a steamship ticket seller on Martha's Vineyard, and at the University of Pennsylvania his thesis was titled A Venture in Marine Transportation.

A bachelor, Snider rents apartments in both Hyannis and Boston. His burgeoning career as a transportation tycoon has done nothing to diminish his wanderlust. "My greatest fantasy," confesses Snider, "is to take a freighter all around South America, the South Seas and Tahiti, then maybe travel the Orient Express. I love to travel," he I rails, "but never by plane."