Getting there
The two parks have genuinely different transport realities — the Peak District is unusually well served by rail for a national park, the Yorkshire Dales much less so outside one specific line. Plan around the actual gaps rather than assuming both work the same way.
By train: the Hope Valley line
The Manchester–Sheffield Hope Valley line runs directly through the Peak District, stopping at Edale, Hope, Bamford, and Hathersage — a genuinely rare case of a national park's best walking trailheads sitting on a regular passenger railway rather than requiring a car. Edale, the trailhead for Kinder Scout and the start of the Pennine Way, is walkable straight from its station platform. Services run roughly hourly on most days, more frequently at peak times, making a car-free day trip from either Manchester or Sheffield entirely realistic.
By train: the Settle–Carlisle line
The Yorkshire Dales' equivalent is the Settle–Carlisle line, a genuinely scenic Victorian railway running from Leeds through Settle, Horton-in-Ribblesdale, Ribblehead, and Garsdale before crossing into Cumbria. It's the only realistic rail option for reaching the Yorkshire Three Peaks trailhead at Horton without a car, and several walkers deliberately use it both ways to avoid the notoriously limited parking there. Services are considerably less frequent than the Hope Valley line — typically a handful a day rather than hourly — so a return time has to be planned around the timetable, not assumed.
By car
The two parks sit roughly 90 minutes to two hours apart by road, typically via the A628/Woodhead route or the M62 corridor depending on which side of each park you're starting from. Within the Peak District, the A6187 through the Hope Valley and the A625/A6187 combination past Castleton carry most visitor traffic and can back up badly on summer weekends, particularly around Ladybower Reservoir and through Castleton itself. In the Dales, single-track roads with passing places are common west of Malham and around Kettlewell — allow more time than a map distance suggests, and expect to reverse to a passing place at least once on a busy day.
Parking realities
Peak District and Yorkshire Dales car parks operated by the National Trust or the National Park Authority are pay-and-display, cash increasingly less accepted than card or app payment — check the specific site's payment method before arriving, since not every rural car park has reliable mobile signal for an app to load. Roadside verge parking is actively enforced against at the busiest sites (Dovedale in particular), with real risk of a fine or clamping rather than an idle threat.