• Cycle Time ($C$ or $T_c$): The total round-trip time for a transit vehicle on a route, including travel time in both directions, layovers at terminals, and dwell times at stops.
• Fleet Size ($N$): The minimum number of vehicles required to maintain the schedule on a route. $N = \lceil C/h \rceil$ (rounded up to the next integer).
• Layover Time: Time built into the schedule at the end of a route to allow drivers a break, absorb unexpected delays, and ensure the vehicle departs the terminal precisely on time for the next trip.

• Short Stop Spacing (e.g., every block): Excellent accessibility for riders (short walking distance), but the vehicle spends a significant portion of its time decelerating, stopping, and accelerating, leading to very low average travel speeds.
• Long Stop Spacing (e.g., miles apart): Excellent mobility and high average travel speeds, but poor accessibility for those far from stops.
• Optimal Spacing: Depends on the mode (local buses require short spacing, BRT requires medium spacing, commuter rail requires long spacing) and the density of the served area. The goal is to minimize total passenger travel time (access time + waiting time + in-vehicle travel time).

• Class C (Mixed Traffic): Transit vehicles share the road entirely with private cars. (e.g., standard local buses, streetcars). They are subject to general traffic congestion, making them the slowest and least reliable, but cheapest to implement.
• Class B (Semi-Exclusive): Transit vehicles have dedicated lanes (e.g., painted bus lanes, raised median tramways) but still interact with general traffic at intersections (which may or may not have transit signal priority).
• Class A (Fully Exclusive): Transit vehicles operate on a fully grade-separated guideway (e.g., subway tunnels, elevated tracks) with no interaction with pedestrians or private vehicles. This provides the highest speed, capacity, and reliability, but is the most expensive to build.

• Paratransit / Demand-Response: Unlike fixed-route buses, these systems dispatch vehicles (often vans or minibuses) based on user requests, providing door-to-door or curb-to-curb service. They are mandated by the Americans with Disabilities Act (ADA) as a complementary service for individuals unable to use the fixed-route system due to a disability. They are highly subsidized and expensive per trip but essential for equity.
• Micro-Transit: A modern evolution of demand-response, often using smartphone apps for dynamic routing of small shuttles in low-density suburban areas or corporate campuses, aggregating riders heading in the same general direction.
• Micro-Mobility: The growing ecosystem of shared, low-speed, lightweight vehicles (like dockless electric scooters and bikeshare systems). These are critical for solving the "First-Mile/Last-Mile" problem, helping users travel the short distance between a major transit hub (like a train station) and their final destination without needing a car.

(Note: $\lceil x \rceil$ means rounding up to the next whole integer, as you cannot operate a fraction of a bus).

The Cycle Time ($T_c$) is the total time it takes one vehicle to complete a full round trip and be ready to start again. It includes:

• Running Time: The actual time spent driving in both directions.
• Dwell Time: The time spent stopped at stations allowing passengers to board and alight.
• Recovery/Layover Time: A buffer time built into the schedule at the end of the line to absorb delays, allow the driver to rest, and ensure the next trip starts on time (typically 10-15% of the running time).

• Radial Networks: Routes converge on a single central business district (CBD) from the suburbs. Highly efficient for downtown commuters but terrible for suburb-to-suburb travel.
• Grid Networks: Routes operate on perpendicular arterial streets, allowing users to reach any point with a single transfer. Common in older, dense cities.
• Hub-and-Spoke Networks: Routes connect outer nodes to major transfer hubs, which are then connected by high-frequency corridors. Highly efficient for operations but increases the transfer penalty for riders.

Dwell time is the largest source of variability in transit operations. It depends on:

• The number of boarding and alighting passengers.
• The door configuration (number of doors, width).
• The fare collection method (e.g., cash payment takes significantly longer than tap-and-go smart cards or off-board ticketing).
• Vehicle floor height (low-floor buses reduce step-up time).

Minimizing dwell time is crucial for improving commercial speed and fleet efficiency.

It grades Quality of Service (QOS) on an A-F scale across two main categories:

• Availability: Is the service there when and where you need it? (Measured by frequency, hours of operation, and spatial coverage/walking distance to stops).
• Comfort and Convenience: How pleasant is the ride? (Measured by crowding/load factor, on-time reliability, travel time relative to driving, and perceived safety).

• High Density: Zoning for high-density residential and commercial development within a 0.5-mile (or 10-minute) walking radius of a major transit station. The density provides the inherent ridership necessary to sustain high-frequency transit service.
• Mixed-Use: Blending residential, retail, office, and recreational spaces in close proximity. This creates a vibrant, 24-hour environment where residents can live, work, and play without needing a car.
• Pedestrian-Centric: Designing streets primarily for walking and bicycling, with wide sidewalks, safe crossings, and limited parking. The "last mile" problem (getting from the station to the final destination) must be seamlessly solved for pedestrians.
• Value Capture: The transit infrastructure increases surrounding land values. Mechanisms like Tax Increment Financing (TIF) capture this increased value to help fund the transit system itself.