Thomas Saf-T-Liner C2

Design and manufacture

As the Thomas Saf-T-Liner C2 marked the first completely new bus body for the company since 1962, Thomas redesigned a number of its manufacturing techniques coinciding with its introduction.

To minimize the number of rivets and welds (a weak point of structural integrity on a bus body), adhesive bonding was used to complete a number of body joints. In the cases where fasteners are needed, self-piercing rivets are used. These engineered fasteners join layers of metal together without punching completely through the bottom layer, thus reducing the likelihood that rivets will become the source of leaks in the future.

Chassis

As with all conventional-style school buses, the C2 is derived from a cowled-chassis conventional; the C2 uses the Freightliner C2 variant of the M2. As with 2000s and 2010s industry practice in school bus manufacturing, chassis and body manufacturers are paired, with Freightliner and Thomas developing the C2 as an integrated vehicle (the Freightliner grille badges are replaced with Thomas badges).

At its launch, Mercedes-Benz MBE diesel engines were the standard engines, with optional Caterpillar C7 and Cummins ISB diesels. In 2008, the Cummins ISB6.7 replaced the MBE900 as the standard engine, with the C7 discontinued. From 2010 to 2018, the sole diesel engine in the Thomas C2 was the Cummins ISB6.7; for 2018 production, the Detroit Diesel DD5 becomes an option.^[7]

The C2 comes standard with an Allison 2500 automatic transmission with an Allison 3000 automatic transmission as an option. The Saf-T-Liner C2 is the only school bus in North America offered with a manual transmission; a rarely ordered option is a Fuller 6-speed transmission.

Body

In a break from traditional bus body design, as body manufacturers acted as second stage manufacturers adapting the body to the chassis, in the design of the C2, Freightliner-owned Thomas Built Buses designed the body and chassis of Saf-T-Liner C2 as fully integrated components. A separate body from the Saf-T-Liner EFX/HDX and Minotour, the C2 body shares no parts with its Saf-T-Liner Conventional/FS-65 predecessor.

While Freightliner has also produced cutaway-cab buses derived from the M2 for commercial/transit use, Thomas Built Buses is the only manufacturer to produce a cowled-chassis bus body derived from the M2. Coinciding with the shift to the Freightliner M2 cowl, several changes were made to improve the functionality over its predecessor. Most visibly, to improve aerodynamics, the traditional multipane vertical windshield was replaced by a sloped single-piece curved piece of glass (allowing the use of the stock windshield wipers).^[4] Above the windshield, the front bodywork matches the windshield slope; to further improve aerodynamics, the warning lamp lenses are faired into the body (where allowed by regulations).

On the rear of the C2, the body also used flush-mounted glass and warning-lamp lenses. While not substantially physically taller than its predecessor, Thomas visually extended the height of the C2 with larger passenger windows than previous school buses, along with larger exit doors.

On the exterior, the C2 has largely remained the same throughout its production run. In late 2007, the passenger windows saw a minor change, with a shift to equal-size window sashes (previously, the top half was larger). In the rear, the taillights were redesigned and enlarged, later becoming a standard design for all Thomas buses. To improve driver sightlines, the mirror bracket for the passenger-side rear-view mirrors was extended forward.

In the interior of the C2, Thomas made many advancements in an effort to maximize parts compatibility between the bus body and donor chassis. In previous conventional-style school buses, from the firewall rearward, only the steering column and instrument cluster were used. With the interior of the Thomas C2, the dashboard of Freightliner M2 is used in its entirety, adopting only minor changes (the ignition switch was required to move to the center of the dashboard, due to a driver control panel replacing the driver-side door).

Along with the optimization of aerodynamics, the body of the Thomas C2 also optimized driver visibility. Following the redesign of the windshield, the entry door was repositioned, creating a large window between the entry door and windshield to view sightlines in the loading zone (a feature adopted from the Thomas Vista and nearly all small school buses); a smaller quarter window was located forward of the driver's sliding window. In comparison to other Thomas buses, the C2 has enlarged passenger windows and larger emergency exits.^[8]

While initially equipped with an air-operated entry door, in 2012, an electric-operated entry door became offered as an option. Since 2016, a manually operated passenger entry door was added as an option.^{[citation needed]}

At the end of 2023, Thomas debuted the Saf-T-Liner C2 Evolved for 2025 production, marking the first major update to the C2 in over 15 years.^[9] While the underlying body structure saw few changes, the C2 Evolved followed suit with the updates of the Freightliner M2 Plus. Along with a digital dashboard and a stalk-operated transmission shifter, the update saw a modernization of the electrical system (allowing for better integration of future technology).^[9] Externally, the C2 Evolved adopted the slatted grille style of the M2 Plus (in line with the larger Freightliner Cascadia).

Alternative fuel powertrains

In May 2014, Thomas Built Buses began production of a propane-fueled version of the Saf-T-Liner C2.^[10] Powered by a 339 hp 8.0L V8, the C2 Propane is paired with the Allison 2300PTS automatic transmission.^[11] The engine is designed by Powertrain Integration (an OEM supplier to General Motors) with the 8.0L V8 named the PIthon.^[12][13] In 2019, the propane engine was enlarged to a DriveForce-branded 8.8 L,^[14] supplied by Power Solutions International,^[15] which had acquired Powertrain Integration in 2015.^[16]

In 2016, a compressed natural gas (CNG) variant of the Saf-T-Liner C2 was released. The first Type C (conventional-style) school bus produced with a CNG fuel system, the Saf-T-Liner C2 CNG is powered by a version of the Cummins ISB 6.7 engine.^[17]

C2e (hybrid-electric bus)

In 2007, Thomas introduced a hybrid-electric version of the Saf-T-Liner, named the C2e (stylized as C2^e). The parallel hybrid drivetrain was designed by Eaton Corporation; the C2e retains the Cummins ISB engine and adds a 1.9 kW-hr lithium-ion battery pack with a 44 kW electric motor/generator.^[18][19][20] Annual fuel savings were estimated to range from 300 to 450 US gal (1,100 to 1,700 L) assuming 10,000 miles (16,000 km) per year.^[21][22] This is a 20% increase in fuel economy, and the buses can drive under battery propulsion for up to 15 miles (24 km).^[23] At least 24 C2e buses were built and delivered to operators in Kentucky and Michigan.^[23][24] In the summer of 2013, Thomas removed the C2e product literature from their website, marking its discontinuation.

C2 Jouley (electric bus)

In November 2018, Thomas unveiled a battery-powered prototype of the Thomas Saf-T-Liner C2 designated eC2 or "Jouley" (after the unit of energy).^[25] The prototype previews an all-electric C2 intended for production during 2019;^[26] it was developed in partnership with Proterra, Inc., who offer a line of transit buses using the same battery-electric drivetrain.^[27] The C2 Jouley uses a single traction motor with an output of 295 / 170 hp (220 / 127 kW) (peak/continuous) and a two-speed gearbox; this configuration is branded ProDrive by Proterra. The traction battery has a total capacity of 220 kW-hr, providing a range of up to 135 miles (217 km), assuming an efficiency of 1.4 kW-hr/mile (24.6 mpg_‑US (9.6 L/100 km) equivalent). The bus is charged using the SAE J1772 CCS Combo 1 connector; a full charge takes approximately 3 hours using a 60 kW DC charger.^[28]

The first large order for 50 Jouley buses was placed by Dominion Energy in December 2019 as the first phase of their school bus replacement program, to be delivered by the end of 2020.^[29] In February 2021, the Montgomery County Public Schools (Maryland), largest school district in the state, announced they had ordered 326 Jouley buses.^[30] On October 17, 2022, Thomas delivered the 200th Saf-T-Liner C2 Jouley to Indiana-based Monroe County Public Schools.^[31]

Other uses

Alongside its yellow school bus configuration, Thomas Built Buses produces multiple configurations of the Saf-T-Liner C2, including MFSAB versions (activity/childcare versions), along with the Transit Liner C2 commercial-use bus. Through aftermarket manufacturers, the C2 also serves as a donor vehicle for multiple types of specialty vehicles derived from bus bodies.^[32]