CHAPTER 4

Capacity Concepts and Analysis Methods: Vehicle Ferries

While many capacity concepts for vehicle ferries are similar to those of passenger-only ferries, there are key differences due to the operational and terminal infrastructure requirements for carrying vehicles. These requirements include larger terminal space requirements for queuing vehicles, the terminal infrastructure for vehicle loading ramps, and coordination with the capacity of connecting roadway infrastructure. While this chapter focuses on capacity concepts and analysis methods for vehicles, the capacity concepts and analysis methods related to passenger facilities and throughput presented in Chapter 3 also apply to most ferry services carrying vehicles and walk-on passengers.

Quantitative procedures outlined in Chapter 4 include those presented in the discussions of Equation 3: Using AEU to calculate vehicle capacity of the vessel, Equation 4: Estimating vehicles left behind, and Equation 5: Sizing vehicle fare collection facilities.

Optimizing the Service Schedule

The following sections identify ways to optimize the service schedule by accounting for the operating margin, reducing dwell time, and using demand management tools.

Operating Margin

Vehicle ferries experience periods of heavy traffic where dwell time takes longer and sailings become later and later until the heavy traffic subsides. Additionally, systems may experience long dwell times due to incidents such as a stalled vehicle or medical emergency. To account for longer-than-average dwell times in the service schedule, vehicle ferry systems must determine the amount of time that accounts for these periods. Scheduling extra dwell time for designated sailings allows ferry service to get back on schedule.

Equation 1 (in Chapter 3) presents a method for assessing operating margin for both passenger-only and vehicle ferries.

Minimizing Dwell Time

For ferries that serve passengers and vehicles, the time required to load and unload vehicles is typically the largest component of dwell time. The design and layout of terminal elements and operational factors can affect the amount of dwell time required for vehicles to load and unload the vessel. Operators responding to the questionnaire provided best practices for minimizing dwell time. Equation 9-4 of the TCQSM (Ryus et al. 2013) provides a procedure for calculating the total time required to load and unload vehicles. Table 16 provides a summary of best practices identified by operators responding to the questionnaire.

Table 16. Summary of vessel loading best practices from operators.

Optimizing Capacity with Demand Management

For vehicle ferry services, vehicle capacity is often reached before passenger capacity. Because of this, shifting riders from their vehicles to walking on the ferry or spreading the peak vehicle demand can help increase the capacity of the system to serve more people without requiring capital investment in new vessels.

Potential demand management strategies that can be used by operators to promote mode shift or spread peak demand, thereby maximizing the use of existing assets, include those discussed in the following subsections.

Mode Split Change Strategies

• First- and last-mile connections: Partnership with transit agencies to improve connections, including synchronization of schedules, can help move more passengers from vehicles to walk-on. Additionally, connections to terminals can be improved through coordination with microtransit and improvements to pedestrian and bicycle connections.
• Pricing strategies: Reducing the cost of walk-on or bicycle fares relative to vehicle fares can promote mode shift to increase walk-on ridership.

Demand and Operational Strategies

• Enhanced user information: Through technological improvements, customers can see when there is space available on the vessel or when there are shorter terminal queue lengths, which can help spread the demand over the day.
• Increase service hours: Capacity of a route or system can be increased through expansion of the service day or increased frequency of sailings. While some service expansion can be realized with existing assets, schedule planning must take into account the maintenance and relief needs through redundancy of the fleet, as discussed in the System Redundancy section of Chapter 2. If mode shift is also a focus for the route, a corresponding increase in service hours for connecting transit modes is required.
• Pricing strategies: Implementation of demand-based pricing, where fares are higher during daily, weekly, or seasonally peak travel times, can help spread and balance demand.
• Terminal operational efficiencies: Implementation of operational efficiencies, such as multiple-lane loading/unloading or synching traffic signals for connecting roadway intersections, can increase how quickly vehicles can be loaded and unloaded at the terminal and increase system and route capacity.
• Vehicle reservation system: Where feasible based on availability of queuing space at terminals, operational and staffing support, and on-time performance of the route, implementation of a vehicle reservation system can spread demand throughout the day by directing customers to sailings with available space.

Table 17. Bicycle management examples – vehicle ferries.

An example of demand management strategy use can be found in the Washington State Ferries 2040 Long Range Plan (Washington State Department of Transportation Ferries Division 2019), where specific strategies are identified as key tools for accommodating future growth.

Bicycle Management for Vehicle Ferries

Considerations for accommodating and managing bicycles include those of safety (maintaining separation between bicyclists and vehicles), dwell time (additional time to load and unload bicycles if separated from vehicles and passengers), and space (storage at the terminal and on vessels).

• Loading and unloading: Bicycles can be loaded over passenger walkways or vehicle ramps.
• Storage on the vessel: How and when bicycles are loaded and unloaded from the vessel are affected by where they are stored on the vessel. On shorter, protected routes such as river crossings, bicycles can be leaned against a rail. In most cases, bicycle storage on the vessel requires racks or designated space. If feasible, bicycle storage on the vessel should provide protection from weather and water spray.

Examples of how different vehicle ferry systems manage bicycles are shown in Table 17.

Understanding Vessel Capacity and Vehicle Demand

The number of vehicles a vehicle ferry can carry depends on several factors, including route-specific trends in volume and type of vehicle demand as well as the vessel capacity and design. Vessel design considerations include the vehicle footprint and space requirements (AEU) as well as over-height or large vehicle capacity.

Providing Space for Various Vehicle Sizes

Ferry operators use different standard footprints, or AEUs, to represent the dimensions of a standard vehicle. In Chapter 9, Section 2, Ferry Service and Facilities, the TCQSM (Ryus et al. 2013) provides factors commonly used to compare different vehicle types to a standard-sized vehicle:

• Standard vehicle = 1 AEU
• Recreational vehicle, single-unit truck, or bus = 3 AEU
• Semi-trailer truck = 5 AEU

Depending on the vessel arrangement, capacity for taller vehicles may be limited due to clearance limits. Vessels that do not have an open vehicle deck, such as those with an overhead bridge or two levels of vehicle space, are likely designed with some sections of lower vehicle height clearance than others. Capacity for over-height vehicles must be accounted for in how

vehicles are arranged in holding lanes (possibly requiring a designated lane) and how they are loaded onto the vessel. Operators may plan additional footprint for over-height vehicles to account for the added space needed for staging. For example, BC Ferries plans use the following factor for planning over-height vehicles:

• Over-height vehicle = 1.5 AEU

While the AEU is a standardized measurement used for planning purposes, for planning and communicating vessel capacity, it is advantageous to use an average measurement that realistically represents the number of vehicles that are typically carried on a route. The size of the AEU for a route depends on factors such as what type of vehicles are popular in the area (sedans or trucks), typical commercial vehicle demand, and typical or seasonal demand for recreational vehicles and trailers. Because of differing vehicle demand profiles, a representative AEU may be different between operators, or even between routes for the same operator. Operators must also plan for the space between vehicles, either by including it in the AEU or accounting for it separately. Typically on vehicle ferries, crews direct vehicles onto the ferry and assist drivers in parking as close to the vehicle in front as possible (leaving escape route space between every vehicle or few vehicles as designated by the Coast Guard requirements for that vessel) in order to maximize capacity and minimize the vehicle loading time. Example AEUs used by operators, as provided in responses to the operator questionnaire or found in ferry service planning documents, are presented in Table 18.

Equation 3 can be used to calculate the standard vehicle capacity of a vessel. The equation can also be applied to estimate the capacity of holding or queuing lanes, although that calculation should include more space between vehicles since drivers park themselves and are likely to leave more space between their vehicles than would be left on the ferry.

Equation 3. Using AEU to calculate vehicle capacity of the vessel.

V_S = L/(AEU + S) + C

where

Table 18. AEU by operator.

Vehicles Left Behind

Understanding the number of sailings where capacity is exceeded and knowing the number of vehicles left behind during peak periods can support informed capacity planning. Methods for calculating vehicles left behind include those discussed in the following:

• Estimated number of sailings where demand exceeds capacity: This is the count or average of the number of sailings over a certain period of time where any number of vehicles are left behind to wait for the next sailing when a full vessel departs.
• Estimated number of vehicles left behind for capacity planning and real-time wait estimation: For routes with low numbers of vehicles left behind, the number of vehicles remaining in queue or holding lanes can be counted. For routes with higher numbers of vehicles left behind where actual counts are impractical, the number of vehicles can be estimated based on the approximate location of the end of the queue and pre-established vehicle estimates. Equation 4 presents a method for estimating the number of vehicles left behind.

Equation 4. Estimating vehicles left behind.

V_LB = L/(AEU + S)

where

Vehicle Terminal Capacity Planning and Minimizing Dwell Time

Capacity planning for vehicle ferry terminals focuses on how many vehicles can be held after fare processing, how they are sorted prior to loading, and how quickly they can load and unload the vessel. Habib et al. (1980) provide a detailed overview of procedures used by urban ferry services for processing and holding vehicles at the terminal as well as loading and unloading vessels. The sections that follow provide an overview of operational and terminal design best practices that can help minimize dwell time and support maximization of vessel berthing capacity.

Sizing the Vehicle Holding Area

Planning for queuing and holding lane capacity depends on a variety of factors, including the types of vehicles that use the ferry and the land uses around the terminal. Providing enough space in the vehicle holding area for more than the vessel capacity brings the vehicles closer to where they will load the vessel and provides flexibility for staging vehicles, both of which can serve to reduce the dwell time. The amount of space planned for vehicle holding depends on vessel capacity and the operational practices of the ferry system, as well as the number of routes serving the terminal. Habib et al. (1980) include the recommendation that terminals be sized for the demand estimated to occur 20 to 25 years after the facility is built and for all uses at any one time, including queued vehicles, park-and-ride use, buses, and passenger and employee

parking. However, historical vehicle capacity guidance may become outdated in areas where ridership is anticipated to shift from personal vehicle use to other modes due to mode shift trends or policy decisions.

Table 19 summarizes the design guidelines for holding area capacity used by three vehicle ferry operators. For terminals served by multiple vessel sizes, holding area capacity is designed based on the capacity of the largest vessel.

Lane width requirements often vary by type of use. For example, WSF designates a minimum holding lane width of 9 feet for general traffic lanes; 10 feet for over-height vehicles, carpool/vanpool, and shoulder holding lanes; 11 feet for service and utility vehicles; and 12 feet for accessible lanes.

Optimizing Vehicle Queuing and Holding Area Configuration

Because the amount of space available for vehicle holding at the terminal is often constrained, operators employ different strategies to optimize capacity and vessel loading. The ability to pre-sort vehicle types prior to loading using a reservation system or multiple parallel vehicle lanes allows for faster vehicle loading to minimize dwell time and maximize system capacity. The rate at which vehicles can move through a terminal facility has a direct impact on dwell time requirements.

Table 20 summarizes best practices for holding area design used by different operators to minimize dwell time.

In addition to optimizing the capacity of holding areas and minimizing vehicle loading time, operators may prioritize certain types of vehicles or users when loading, allowing them to move ahead of the general queue and requiring a separate holding area. Operators may choose to designate holding lanes for specific uses, depending on route context and policy decisions, as well as to allow for increased flexibility during vehicle loading. Figure 8 illustrates considerations that affect how much terminal space and how many holding lanes are needed, as well as potential uses that may be given designated lanes or priority loading.

Expediting Fare Collection and Passenger Counting

Fare collection methods and technologies used and the location of fare collection relative to vehicle holding or loading can affect the dwell time and overall capacity of the ferry system. Specific fare processing times depend on the operating systems and policy. For example, the time required for cash transactions can be minimal if exact fare is required, and credit and debit card processing time can vary widely depending on the speed of the network connection

Table 19. Example holding area capacity standards.

Table 20. Best practices for maximizing holding area capacity.

and transaction validation requirements. Table 21 provides examples of the time required per transaction based on the type of fare, as presented by Habib et al. (1980).

The average vehicle processing rates experienced by each operator depend on a number of variables, including the rates of use of reservations, credit cards, and multi-fare passes. As an example, the WSF Terminal Design Manual (Washington State Department of Transportation Ferries Division 2016) provides an average vehicle processing rate for planning purposes of 2.5 vehicles per minute per toll booth, or 150 vehicles per hour per toll booth, although it is noted that actual rates vary between terminals and throughout the day.

Table 21. Fare collection transaction time (Habib et al. 1980).

Planning Vehicle Fare Collection Facilities

A method for calculating the number of toll booths needed to provide a targeted vehicle processing rate during the peak hour can be calculated using Equation 5. This method assumes that holding area capacity can accommodate at least a full vessel load of vehicles. For terminals serving multiple routes, additional holding area capacity and fare processing capacity are required to process vehicles arriving at the terminal for different sailings.

Equation 5. Sizing vehicle fare collection facilities.

T = V(F_N)/R

where

Fare Collection and Passenger Counting Methods

Because of the Coast Guard requirement that all passengers be counted, including those riding in vehicles, implementation of technologies for automated fare collection such as license plate readers or radio transponders that could speed up fare collection and reduce dwell time is challenging. Review of potential technologies and alternatives for automated vehicle fare processing is recommended for further research.

Other opportunities to reduce the time required for fare collection, thereby minimizing dwell time and maximizing system capacity, are presented in Table 22.

Planning for Terminal Compatibility

The capacity of the intersections and roadways connecting to the terminal must also be accounted for in ferry system capacity planning. If roadway connections outside of the terminal cannot accommodate vehicles at the rate at which they unload from the vessel and exit the terminal, backups can occur, which may delay vessel unloading and cause unacceptable levels of traffic disruption near the terminal. This is a greater concern for higher-capacity systems with vessels that carry a large number of vehicles.

Considerations and best practices for coordinating the capacity of multimodal connections for passengers are addressed in the Multimodal Connections section of Chapter 3.

Connecting Roadways

At most ferry terminals, unloading vehicles exit the terminal at a single point, and all unloading vehicles must clear the area near the vessel before vehicle loading for the next sailing can begin. Therefore, the capacity and timing of the intersection nearest to the terminal is a key capacity

Table 22. Vehicle fare collection and passenger counting best practices.

planning consideration for vehicle ferry services. Unless all unloading vehicles can be accommodated in exit lanes before the nearest intersection, there is potential for that intersection to become a limiting factor in terminal throughput.

The rate at which vehicles load and unload varies by system. For example, the Lummi Island Ferry System Level of Service Alternatives Analysis (Whatcom County Public Works 2018) uses a rate of 10.7 vehicles per minute (or 5.6 seconds per vehicle) per ramp lane for loading and unloading. Factors that may affect the rate at which vehicles unload from the vessel include the type of ridership (regular commuters or first-time users), the number of large or over-height vehicles, the number of vehicle lanes on the ramp, and the design of lanes (straight or curved).

Potential opportunities to address capacity issues in connecting roadways and intersections are presented in Table 23.

Table 23. Best practices for coordinating capacity with connecting roadways.