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Communication Technologies
Fact Sheet: Transit Overview

Technology Overview

Use Communications Technology for:

  • Dispatching and schedule adjustments
  • Route deviation and dynamic rerouting
  • Incident notification and emergency response
  • All communication between transit staff, including
    drivers, dispatchers, operations and maintenance personnel

Transit communications systems are technologies that pass information from one user to another in a useable form via wire, wireless, radio, the Internet or other links. Communications technologies facilitate interaction among drivers, dispatchers, emergency responders and other personnel involved in transit and transportation operations. Typically, basic transit communications start with the conventional land mobile radio system (LMRS), which is a wireless communications system used by transit organizations to communicate with field personnel. Communication is typically over digital and/or analog radio. Most current communications systems can be used to transmit voice, text, data, and video, while advanced communications systems are now enabling remote vehicle control. Both voice and text data can be transmitted over digital radio, the Internet, cellular, or other wireless networks. Preprogrammed text messages can be sent between drivers and dispatchers using a range of devices.

Mobile data terminals (MDTs) or mobile digital computers (MDCs) are computerized devices used in public transit vehicles to communicate with a central dispatch office. MDTs provide two-way, text-based communications and the ability to upload data collected during a scheduled run. A radio communications system consists of fixed- and mobile-radio equipment designed to serve an organization by allowing specific communications modes between dispatch and operators on a one-to-one basis or one-to-many basis. Common radio communications systems use one or more fixed sites that have the ability to repeat and relay messages to nearby and remote sites as needed. Many frequency bands and modulation types are used for radio communications systems.

image showing MDC mounted onboard a bus

Mobile digital computers (MDCs) are mounted
onboard transit vehicles and communicate with
the dispatch office to transmit and receive
real-time updates to scheduling, such as an added
trip or missed passenger pickup. They also replace
the driver’s paper records of activity on a shift.

Wireless communications technologies allow for electronic communications that do not utilize cables or wires. Radio frequencies are used to send messages from one device to another. The most common wireless communications technologies are short message service (SMS), general packet radio service (GPRS), 3rd/4th generation (3G/4G) mobile telephony, dedicated short range communications (DSRC), Wi-Fi, and Bluetooth. SMS, a form of text messaging, is a service for sending short messages of up to 160 characters to mobile devices. GPRS is a packet-based wireless communications service that provides data rates from 56 kbps up to 114 kbps and continuous connection to the Internet for mobile phone and computer users. Newer communications technologies provide even higher data rates and enable videoconferencing and interacting with multimedia websites. 3G/4G mobile telephony provides wireless users with faster access to the Internet. DSRC enables wireless communications over distances of less than 1,000 feet.

A comprehensive system that combines various communications technologies will allow interaction among the widest range of communications and data systems, as well as among transportation operators, including across multiple modes. Many transit agencies ban the use of cell phones by transit operators to enhance passenger safety; therefore, dispatchers rely on radio systems to communicate with transit operators. It is important for a transit agency to maintain backup power for all segments of its communications network. Interoperability of communication systems is essential for emergency responders during an incident. It is crucial for transit operators to be able to work seamlessly with fire and police departments when responding to incidents on the transit system. Interoperability also allows a transit agency to maximize resources for planned events.

Types of communications:

  • Vehicle to dispatch
  • Train-location monitoring
  • Vehicle identification and routing
  • Emergency remote train control and emergency notification

Preprogrammed text messages can be sent between drivers and dispatchers using a range of devices. MDTs provide two-way, text-based communications and the ability to upload data collected during a scheduled transit route. The use of MDTs for standard communications purposes minimizes reliance on voice-based communications in large, urban areas where bandwidth is scarce. Voice communications are still used when preset MDTs messages are insufficient. Large transit agencies often install both voice and text communications devices. However, a voice-only system is usually sufficient for smaller transit agencies.

image showing MDC mounted onboard a bus

Los Angeles County Metro Rapid Bus Operations Control Center

Replacing public switched telephone network (PSTN) lines between facilities with voice over Internet protocol (VoIP) for phone calls can help reduce trunking, long-distance phone charges and server costs. By using just a single data pipe, VoIP utilizes a packet-switched network instead of the circuit-switched voice transmission lines employed by traditional telephone networks. VoIP needs an Internet connection to work and VoIP will not work during a power failure unless the VoIP operator offers backup power. VoIP can simplify and lower the cost of networking multiple facilities in different locations, for example, agencies that have multiple call centers or maintenance facilities separated from operations centers. Service and support is simplified since VoIP uses the same cabling as computers (CAT 5 or CAT 5e Ethernet cables that facilitate high-speed digital data and voice connectivity through an RJ-145 connector).

Common Combinations

Daily Operations

Communications systems, particularly MDTs, are often integrated with computer-aided dispatch and scheduling (CADS) systems by medium to large transit agencies. This combination allows dispatchers to make optimal changes to itineraries when necessary and to automatically communicate updated information to drivers. Communications systems can also be integrated with automatic vehicle location (AVL) systems to provide real-time location data with every communication exchange. This information can be transmitted in voice or text form.

Transit AVL/Advanced Communication System

California PATH Program Communications System

Safety and Security

Communications systems can be installed with a dedicated channel for emergency response. MDTs can include a preprogrammed emergency message that when integrated with AVL technologies can help provide location and pertinent information about a distressed vehicle. In addition, a silent alarm or closed-circuit television (CCTV) camera video feed from a transit vehicle or transit facility to the operations or security center will utilize the communications network, which must be configured to handle video streaming.

Systems Planning and Fleet Management

Communications systems can help combine data gathered by MDTs-AVL system combinations and link the operations data to the transit agency’s geographic information system (GIS) to be analyzed for long-term planning and service adjustments. This data could include real-time ridership figures generated by advanced passenger counters (APCs) that can be used for long-range service planning or in the short-term by operations supervisors to add vehicles when demand outpaces the current in-transit capacity.

Factors to Consider

Communications technologies are vital to any transportation agency; the question is what level of sophistication is right for your agency? For small transit agencies, simple voice communications via cell phone or radio may be sufficient, though many agencies have restrictions on cell phone use while operating transit vehicles and the Federal Motor Carrier Safety Administration (FMCSA) prohibits their use by bus operators of services that cross state lines. Before deploying any new communications component or network, it is important that planning, implementation, and integration be instituted to reduce adverse impacts and maximize the performance from the new communications system.


  • Develop a structured procurement plan and performance-oriented requirements and specifications.
  • Involve staff from various departments and outside stakeholders, such as contractors that may provide transportation services or may be (eventually) linked to the transit agency’s service and communications network.
  • Visit transit agencies providing similar transportation services and discuss their communications networks and application of communications technologies.


  • Perform rigorous testing of the entire system to identify gaps in cellular or radio coverage (identify blackout or dead geographic areas).
  • Consider installing a backup communications system to ensure uninterrupted communications in case of failure by the main network.
  • Consider installing backup power in case of a power failure.
  • Develop standard data-exchange protocols to be able to add equipment from multiple vendors, operate on different bandwidths, and communicate with different technologies using Transit Communications Interface Profiles (TCIP).
  • Equip all systems with virus and firewall protection.
  • Expect a learning curve as drivers and dispatchers develop efficient communications techniques.


  • Communications is being decoupled from AVL-CADS-MDT to allow open standards. Agencies should expect such a multisystem deployment to allow modular implementation and simplified upgrading of other technologies.
  • Transit communications should be linked with the communications networks used by information technologies.

Benefits and Costs


  • The majority of benefits accrue to transit users when communications improve reliability and on-time performance. Communications systems also enhance the safety and security of drivers and travelers. While communications cost savings are possible if communications systems are used to improve adherence to schedules and vehicle-use efficiency and to provide smooth data exchange.
  • The Ann Arbor Transportation Authority (AATA) reported that its on-time departure rate nearly doubled over a 2-year period after the upgrade of its communications system, which included new MDTs.

Other Possible Benefits

  • Decreased emergency response time.
  • Improved customer satisfaction and ridership through better on-time performance.
  • Greater coordination with other regional transit/transportation providers with integrated or interoperable communications networks.


Communications system deployment costs can incorporate many components, including dispatch center hardware and software, data computers, field transmittal devices such as radio towers and fiber-optic cable, and in-vehicle hardware and software such as radio, MDTs, AVL-GPS and other integrated systems. When considering costs for a new communications system or system upgrades, do not forget to account for hidden costs. Factors such as driver and operator training, data storage, and equipment maintenance and support all should be considered as part of the cost of operation. Routine maintenance of all systems should also be taken into account.

Equipment and Implementation

UMN TSP system using AVL/GPS and wireless communications

UMN TSP system using AVL/GPS and wireless

  • The capital cost of equipment and the implementation of communications equipment will vary by transit agency. It is important to use open bid practices to ensure the best value for systems being installed. Detailed requirement documents and test plans will ensure that the agency is well protected. Requiring system block diagrams and making sure that the transit agency maintenance personnel work with the contractors will also ensure a smooth turnover of equipment to the agency upon completion of the installation and testing. Consider adding system warranty periods (3 months to 1 year) to the project following equipment installation acceptance.
  • Requiring a contractor to bench test equipment prior to installation can also help to avoid problems when integrating different systems at the control center, transit stations and on transit vehicles.
  • Hiring a system integrator to be responsible for the overall system can help a transit agency ensure a smooth transition to new communications systems.

Operations and Maintenance (O&M)

  • Expect monthly or annual fees from equipment vendors for MDT system software support.
  • Setting up maintenance management systems that track equipment, repair and maintenance schedules can also have an added benefit when preparing yearly budgets.


  • For MDT staff training, expect an average of 4 hours of training for each vehicle operator.

Distracted Driving

  • Following a series of crashes, agencies are wary of potential distractions for transit operators.
  • Proper training and rules can help avoid safety related incidents.

Agency Deployments

Agency Contact Information Number of Vehicles Context / Success of Deployment
Utah Transit
Authority (UTA)
3600 South 700 West
Salt Lake City, UT 84130
415 buses,
69 light rail cars,
420 vans (12–15 passengers)
Integrated communications system with their public safety program.
Ann Arbor Transportation Authority (AATA) 2700 S. Industrial Hwy.
Ann Arbor, MI 48104
80 buses Integrated MDTs and radio communications with traveler information and AVL.
Los Angeles County Metropolitan Transportation Authority (LAC MTA) One Gateway Plaza
Los Angeles, CA 90012
2,089 buses,
118 light rail cars,
70 heavy rail cars
Integrated AVL and CAD along with APC and a new regional digital 800MHz radio system.
Washington Metropolitan Area Transit Authority (WMATA)
Washington, DC
600 Fifth Street, NW
Washington, DC 20001
1,242 buses,
850 heavy rail cars
Installed a LAN and WAN to support its communications system.

Additional Resources


Jonathan Walker, P.E., Ph.D.
Chief Policy, Architecture, and Knowledge Transfer, ITS Joint Program Office
U.S. Department of Transportation
(202) 366-2199

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