By Richard YS

AN ENDURING WORKHORSE

Ask any bus enthusiast which make and model of bus is most associated with intercity bus travel in North America over the last 30 years, and the answer you’ll most likely hear from them is the MCI D-series coach. First introduced in 1992 as North America’s first 45ft (13.7m) long motorcoach and still being produced today, it is arguably the most successful coach bus in modern times, with a reputation for reliability and durability. The original MCI 102-DL3 (later called the D4500) began the industry’s transition from 40ft long coaches to 45ft long coaches, and its success has spawned many derivative models. The MCI D-series coach has been widely adopted and heavily used across the United States and Canada by intercity providers such as Greyhound, numerous charter companies, as well as public transit agencies for use on regional and commuter routes. As one of the larger regional transit providers in North America, GO Transit has purchased more than 500 MCI D-series coaches since their first order in 2001, with another 177 units currently being delivered or on order.

THE D4500: NEW VEHICLES FOR A TIME OF CHANGE

The first of GO’s MCI D-series coaches were a group of fourteen D4500 coaches numbered 2100-2113 [3]. Their arrival coincided with the beginning of a significant shift in the mode of operation for the GO bus network. Prior to 2000, as detailed in the ‘50 Years of GO Transit Bus Operations’ article by Adam Zhelka, the service provided by GO’s bus operations were mostly train-meet services and train-bus services which ran along GO Train corridors during off-peak hours. GO was also responsible for providing some local service in the York and Durham areas at a time when responsibility for local transit in those areas was divided among the different towns and cities in that region.

But at the turn of the millennium, the situation changed drastically. The opening of Highway 407 allowed the introduction of new regional GO bus routes encircling the City of Toronto through Peel and York Regions and on to Hamilton. The new 407 GO Bus services significantly improved connectivity between the rapidly developing northern and western suburbs as well as to and from many major universities in that corridor. At the same time, newly formed regional agencies such as YRT and DRT in York and Durham, respectively, began to take over many of GO’s local services there. These changes began to shift the GO bus network from a commuter and suburban service to a true regional and intercity operation. The clientele served by GO’s bus network also began to include university students and inter-city vacationers in addition to commuters. Over the subsequent years, as train services expanded to all day service (thus reducing demand for GO buses along former peak-only GO Train corridors), and new inter-regional and inter-city GO bus routes were introduced, ridership from these long-distance travellers increased dramatically. The D4500, with its greater seated capacity of 57 passengers, higher capacity for underfloor luggage, and accessibility through wheelchair lifts, were well-suited to handle the new longer-distance ridership patterns.

Starting with their first order in 2001 through 2004, GO would acquire 167 classic D4500 units. The long, Greyhound-styled coaches quickly became the face of the GO Transit bus network as older coaches and ‘suburban’ style transit buses were retired. In 2005, MCI redesigned the D4500 with a more aggressive-styled front headlight cluster, descended from the MCI G-series intercity coaches built for Greyhound. From this point onwards GO would buy 352 of these restyled D4500CT (CT for ‘contemporary’ styling) coaches until 2015, for a total of 519 total D4500 coaches. Coaches built after 2007 also feature a redesigned rear end with a triangular taillight cluster and improved radiator packages. Some of these ‘contemporary’ styled coaches would end up replacing the older ‘classic’ D4500 coaches in the early 2010s. The last two orders of the D4500 fleet, 2554-2606 and 2607-2616, delivered in 2014-15, featured improved interiors with sleeker luggage racks and reading lights, improved seats, and were delivered in GO’s two-toned paint scheme, which was introduced in 2013 [3].

Over the course of the production run for the GO Transit D4500 fleet, the mechanical aspects of the buses were indicative of the industry typicals of the time of the orders. The earliest D4500s came equipped with Detroit Diesel Series 60 engines. Starting with the 2004 order, the CAT C13 engine was the standard engine that GO specified for their buses. Later, beginning in 2009, the Cummins ISM, and eventually the Cummins ISX, became the standard powerplant on D4500s, although the early-2011 orders of D4500CTs came once again with Series 60 engines. Most units were driven through Allison B500 automatic transmissions, although two orders of D4500s ended up delivered with different powertrain setups [3]. The 2004 D4500s were ordered with the automated-manual ZF AS Tronic 10-speed (later 12-speed) transmissions, which was advertised as more fuel efficient due to their lighter weight. Two of the D4500CTs ordered in 2008 were equipped with the Allison EP50 power-split hybrid electric drivetrain as a test, with the hybrid drive system touted as more fuel-efficient relative to straight diesel coaches. Ultimately, neither the automated-manual transmission nor the hybrid setup seemed to be successful in GO Transit service, as subsequent new orders continued to use the conventional diesel engine with Allison automatic transmissions.

The 519 D4500s acquired by GO Transit between 2001 and 2015 constitute the first generation, or ‘legacy’ fleet of GO’s MCI D-series lineup.

DOUBLE DECKERS CHALLENGE MOTORCOACH DOMINANCE

Throughout the mid-2000s and into the 2010s, the D4500 series coaches were the face of the GO bus network, providing both suburban-commuter services as well as inter-regional services along the 407 corridor. However, with ridership steadily increasing on the inter-regional routes, particularly those serving universities in the Toronto suburbs, GO began to look at double-decker buses as a means of coping with crowding on those services. From 2008 to 2015, 128 standard and lower-height double-decker buses would be purchased by GO, primarily for use on the 407 corridor as well as new intercity routes into Waterloo Region and Niagara Falls, displacing the once-dominant D4500s that once plied these routes.

These double-decker buses were however limited by their height, which prevented them from operating into many of GO’s key destinations such as Union Station or Hamilton GO. This changed in 2016, when the first of 270 ‘Super-Lo’ double-decker buses began to be put into service. Between 2016 and 2021, all orders for new GO buses were of the ‘Super-Lo’ double decker vehicles. Also part of the motivation of GO ordering only double-deckers was to benefit from their low-floor design on their lower levels, which sped up the boarding process for AODA passengers and those with luggage compared to the D4500s’ wheelchair lifts. These ultra-low height double-deckers, which could serve any destination the D4500s already served but also came with a dramatic increase in passenger capacity, displaced and subsequently retired most of the D4500 fleet, though at the time of writing (January 2026) around 150 D4500s were still in service [3].

THE NEW GENERATION: THE D45 CRT

Throughout the production life of the MCI D-series, MCI has constantly made improvements to the coach lineup. As discussed above, over the course of the 2000s the D-series coaches evolved to become sleeker on both the outside and the inside, improving curb appeal and passenger comfort. However, over the production run of the ‘legacy’ D-series coaches from 1992 to 2021, the basic platform has remained the same [2]. That was to change dramatically in 2017, when MCI introduced a low-entry version of the D-series coach to better suit the needs of the commuter coach market.

This radically redesigned coach, designated the D45 CRT LE (CRT for Commuter Rapid Transit, LE for Low-Entry), was designed specifically to allow passengers with mobility aids to enter and exit the coach faster than with traditional lifts [2], but at the expense of reduced luggage storage. The new coach, with its middle door and low-floor section, looked very different from the ‘legacy’ D-series coach. Rather than simply installing a low-entry centre entrance to a D4500, the new coach had more resemblance to MCI’s luxury product, the J4500, itself descended from the original 102-DL3 as well as the MCI 102-EL3 luxury touring coach. Indeed, the D45 CRT LE was developed based on the MCI J4500 platform, but with an eye towards maintaining the D-series’ reputation for reliability and durability. This was done for the D-series lineup to meet new safety standards, raise manufacturing commonality, and improve passenger experience [1]. As a result, the D45 CRT LE incorporated the improved chassis and suspension found on the J-series, in turn improving the handling and ride quality significantly.

Subsequently, MCI made the decision to develop new ‘Next Generation’ D-series coaches based on this new platform to replace the first-generation D-series coaches in production. By 2021, this was finally realized. The D4505 was replaced by the D4520, and the D4500 was replaced by the D45 CRT in MCI’s motorcoach lineup. The D45 CRT and D4520 share the same aesthetics as the D45 CRT LE but lack low-entry sections in the coach midship and instead come with centre (D45 CRT) or rear (D4520) lifts.

MOTORCOACHES RETURN TO GO TRANSIT

By the mid-2020s, GO Transit was again in need of new buses. Despite the COVID-19 pandemic, GO bus ridership quickly recovered after the pandemic, and then dramatically increased, despite an equally dramatic increase in the number and scope of off-peak and weekend GO Train services. The GO bus network now stretched from the Brantford/Six Nations of the Grand River area and the Kitchener-Waterloo Region to the west, to Peterborough in the east. New routes were being introduced along inter-regional and intercity corridors to serve important destinations such as universities, community hubs, and Pearson Airport. GO bus trips serving the Waterloo and Niagara areas became so heavily used that many of the scheduled trips on these routes operated as two- or three-bus convoys. At the same time, GO began to experience increased mechanical difficulties on their double-decker fleet, contributing to a bus shortage relative to demand. GO therefore needed a significant number of new buses to accommodate the new demand as well as to alleviate mechanical issues of an older fleet.

In 2025, GO Transit made an order for 177 MCI D45 CRT coaches, to be delivered between 2025 and 2027, and could be expanded in scope in the future. Despite the availability of the D45 CRT LE low-entry coach, GO still settled for traditional lift-equipped highway coaches. It is speculated that this was due to the low-entry coach’s reduced overall passenger and luggage capacity, since more passengers and their luggage (which need to be stowed in luggage compartments) were now travelling longer distances on the GO bus network. It was originally planned that these new buses would replace the older D4500s, but with the dramatic increase in ridership, the new D45 CRTs would be used to expand service instead, with the D4500s going into second refurbishments instead of being retired.

The first D45 CRTs entered service with GO in December 2025. At the time of writing (January 2026), more D45 CRTs are being placed into service every week. The powertrain of the new coaches is not that different from the last orders of the first-generation D4500s that GO received; they are powered by Cummins X12 engines (an improved version of the ISX used on the D4500s) driving the rear wheels through an Allison B500 automatic transmission. Onboard the new coaches, the improvements MCI made to the D-series is clearly shown through the passenger experience; the coaches are noticeably smoother riding, and the interior appears much more modern and sleek with a spiral entranceway and airline-style curved luggage racks. New conveniences, such as USB chargers, also help make the passenger experience more pleasant than the older fleet. Finally, the coaches feature larger underseat luggage bays, enabling them to carry more suitcases and other luggage, thereby making the D45 CRTs well-suited to serve the current long-distance clientele of GO’s bus network.

THE D-SERIES LEGACY

Since their introduction in 2001, the MCI D-series coach has been an integral part of GO’s bus operations. Throughout the years, they have ebbed and flowed with GO Transit’s ridership patterns and operational needs. Though briefly eclipsed by the double-decker buses in prominence in the mid-2010s, their contribution to the GO bus fleet is undeniable, and with more units now on order, the MCI D-series is poised to once again become the face of the GO Transit bus fleet.

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MCI D-Series Coaches Image Archive

	GO MCI D4500CT 2327 departing Square One for Pearson Airport and Richmond Hill on route 40 HAMILTON-PEARSON AIRPORT-RICHMOND HILL on May 2, 2018. This D4500CT features the redesigned front end with the aggressive-styled headlights, but still featured the older vented rear end design. Photo by Richard YS.
	GO MCI D4500CT 2610 is seen laying over at Burlington GO on May 25, 2025. 2610 is part of the last order of first-generation D4500 coaches. This last order uniquely features an LED headlight array with a black headlight housing, giving the coach an even more aggressive look. Photo by Richard YS.
	GO MCI D4500CT Hybrid 3001 departing Unionville GO on a route 52 OSHAWA-HIGHWAY 407 run on June 14, 2019. 3001 is one of two D4500s in GO's fleet that was ordered with the Allison hybrid system. This bus was retired not long after this photo was taken by Richard YS.
	GO MCI D45 CRT 5007 arriving at Richmond Hill Centre on route 40 RICHMOND HILL-PEARSON AIRPORT-HAMILTON service on January 10, 2026. The radically different styling of the D45 CRT coach can be clearly seen in this photo, taken by Richard YS.

References

1. J. Wang, ‘The new Workhorse of the Motorcoach industry| MCI’s New D model,’ May 2024, Available Online (https://www.youtube.com/watch?v=gg1FgOWgJQE)
2. L. Plachno, ‘D is for Durability - Introducing the New MCI D4520,’ International Bus Trader, pp. 16-21, August 2021
3. Staff, ‘GO Transit - CPTDB Wiki’, Available Online (https://cptdb.ca/wiki/index.php?title=GO_Transit)