Dynamic Brakes: An Important Safety Feature
Last revised: November 2, 2024
By: Adam Burns
While there have been technological improvements to diesels since the 1930s the application of dynamic braking since that time has been the same; a locomotive's traction motors are used to assist in slowing a train when either negotiating a steep grade or for whatever means necessary.
This idea was first put into practice with Electro-Motive's earliest cab designs and became an instant success since it vastly improved safety.
As locomotives have become larger and more powerful over the years dynamics have likewise improved. This was especially true when EMD unveiled its version of the road-switcher in the late 1940s, the GP7, designed primarily for freight service.
During an era when the concept was still new and not entirely proven, most manufacturers offered first-generation models with the option of dynamics. Today, however, they are virtually standard on all new locomotives and have become practically as common as the air-brake.
A trio of Milwaukee Road "Little Joes," with E-20 closest to the photographer, were photographed here at Alberton, Montana in August of 1972. The third unit appears to have its pans down and is not in operation. American-Rails.com collection.The concept of dynamic braking is totally in the realm of diesel locomotives, nothing of the sort was a remote possibility with steam power since it did not utilize any type of electrically operated equipment as a means to generate forward motion.
The first dynamics were available on the initial line of diesels, Electro-Motive's revolutionary FT cab model. During its six-year production run the design sold more than 1,000 examples although, interestingly, back in that era dynamics were not universally accepted as a standard feature.
Instead, many lines only purchased units with dynamics if they were operating in mountainous territory (such as the Pennsylvania) and some roads which did not have significant grades of any kind simply didn't order the feature at all such as the Soo Line or Florida East Coast.
Additionally, others didn't feel the need to operate dynamics on passenger trains, which normally did not require such features. In any event, railroads were still impressed with dynamic braking and its advantages.
The concept is completely oblivious to bystanders and works whereby the electricity flowing to the locomotive's traction motors is reversed turning them into generators through the rotation of the wheels. If you are standing trackside and they are engaged a noticeable humming can be heard.
In other words, instead of electricity powering the motors they actually create it which causes them to resist rotation. This works by the prime mover becoming disconnected from the traction motors and then resistors are switched on.
As a result the force of the spinning wheels cause the motors to generate electricity, which creates enormous amounts of heat that must dissipated via resistors and gigantic fans located on the locomotive's roof.
Up in the cab the engineer has an eight-notch "d.b." (short for dynamic brake) controller, not unlike that of the throttle. The higher this is set the greater amount of electricity the traction motors are asked to make, which further retards the train's speed.
While dynamic braking (which can be engaged as low as 6 mph) does help control a train, whether that be a heavy freight or otherwise, it is only an added safety measure in doing so and is not a replacement to air or pneumatic braking.
As the development of the diesel progressed through the 1960s and second-generation power was unveiled railroads began purchasing "d.b." units in greater numbers, shedding the original notion of utilizing them only in mountainous territory.
This was due primarily for greater operational flexibility by allowing power to roam the system wherever it was needed instead of being restricted to a particular region.
The original concept of dynamic braking was first pioneered years earlier with electric locomotives, which became a common form of road power during the late 19th and early 20th centuries.
Electrics utilized what was known as regenerative braking, which worked very similar to dynamics. However, it was much more efficient; instead of dissipating the energy as heat this type of system returned it as power back to the source (normally a substation) via the overhead catenary.
This allowed the newly generated electricity to then be used by other locomotives.
Such efficiencies and advantages with electrified operations, among others, makes one wonder why it has not been more widely adopted by American freight railroads (the last to employ regenerative braking on a daily basis was the Milwaukee Road on its western Pacific Extension).
An Electro-Motive builder's photo featuring freshly-outshopped Boston & Maine GP9 #1701 in early 1957. Early first-generation models like the GP7 and GP9 could be equipped with or without dynamics.For Electro-Motive, the spotting features of dynamic brakes on its early first, and second-generation road-switchers were located behind the cab. Near the top of the carbody at roughly the center, and just below the roof, is an outward bulge where the resistors are located.
After more than 30 years the location of this classic feature changed with the release of the SD50 in 1981. Now, EMD models such as the newer SD70ACe, sport dynamics further forward and very near the cab; the bulge is no longer present although a stepped roofline and a boxed grill here gives away its location.
For General Electric, dynamic braking on its models has almost always been located towards the rear of the long-hood. These can be located on today's newest units like the ES44AC, ES40DC, and ES44DC under the flared radiator housing via angled grilles.
Depending on your interest level of locomotives, and diesels in particular, a few books on the subject which may be of interest include Mike Schafer’s Vintage Diesel Locomotives and J. Parker Lamb's Evolution Of The American Diesel Locomotive.
As the title suggests Mr. Lamb's book provides a general history of the diesel through the years. In the case of Mr. Schafer's book, it is not particularly long (less than 100 pages) but it is nevertheless pretty interesting!
His title provides a quick look at several classic diesel models from early Electro-Motive products to venerable designs by Baldwin, Fairbanks Morse, and the American Locomotive (Alco).
Recent Articles
-
U.S. Rail Traffic Shows Continued Strength in Week 27 Of 2026
Jul 16, 26 11:52 AM
The Association of American Railroads (AAR) released its weekly rail traffic report on July 15, 2026, covering data for the week ending July 11, 2026 (Week 27). -
DL&W's Tavern-Lounge Observation Cars
Jul 15, 26 10:06 PM
The tavern-lounge-observation cars on the Delaware, Lackawanna & Western Railroad’s (DL&W) Phoebe Snow were signature tail-end cars (numbered 789 and 790), not built by Pullman but by the Budd Company… -
B&O Railroad Museum Rebrands
Jul 15, 26 03:23 PM
The historic B&O Railroad Museum, long celebrated as a cornerstone of American railroad heritage, announced on July 14, 2026, that it is changing its name to the National Museum of Railroad History… -
Amtrak’s Empire Builder – Complete Scenic Route Guide 2026
Jul 15, 26 12:56 PM
Complete 2026 guide to Amtrak’s Empire Builder. Route overview, best scenic sections, schedules, what to expect, and tips for riding this iconic long-distance train through the northern United States. -
Washington ~ Wine Tasting ~ Train Rides
Jul 15, 26 11:39 AM
Here’s a detailed look at where and how to ride, what to expect, and practical tips to make the most of wine tasting by rail in Washington. -
Kentucky ~ Wine Tasting ~ Train Rides
Jul 15, 26 11:37 AM
Kentucky, often celebrated for its rolling pastures, thoroughbred horses, and bourbon legacy, has been cultivating another gem in its storied landscapes; enjoying wine by rail. -
Best THE POLAR EXPRESS™ Train Rides Across the United States 2026
Jul 15, 26 11:04 AM
Discover the best THE POLAR EXPRESS™ Train Rides in the US for 2026. Top locations, what to expect, dates, and tips for this magical holiday experience based on the beloved story. -
Indiana ~ Murder Mystery ~ Dinner Train Rides
Jul 15, 26 09:20 AM
This piece explores the allure of murder mystery trains and why they are becoming a must-try experience for enthusiasts and casual travelers alike. -
Ohio ~ Murder Mystery ~ Dinner Train Rides
Jul 15, 26 09:14 AM
The murder mystery dinner train rides in Ohio provide an immersive experience that combines fine dining, an engaging narrative, and the beauty of Ohio's landscapes. -
Arizona ~ Wild West ~ Train Rides
Jul 15, 26 09:06 AM
Let's delve into the captivating world of Arizona's Wild West train adventures, currently offered at the popular Grand Canyon Railway. -
Michigan ~ Wild West ~ Train Rides
Jul 15, 26 08:49 AM
While the term 'wild west' often conjures up images of dusty plains and expansive deserts, Michigan offers its own unique take on this thrilling period of history. -
Amtrak’s Coast Starlight – Complete Scenic Route Guide 2026
Jul 14, 26 02:24 PM
Complete 2026 guide to Amtrak’s Coast Starlight. Route highlights, best scenic sections, schedules, what to expect, and tips for riding one of America’s most beautiful long-distance trains. -
Best Steam-Powered Scenic Train Rides in the Eastern U.S. 2026
Jul 14, 26 01:21 PM
Discover the best steam-powered scenic train rides in the Eastern U.S. for 2026. From Cass Scenic Railroad Shays to Strasburg and other heritage steam operations — schedules, highlights, and tips. -
Indiana - Beer Tasting - Train Rides
Jul 14, 26 12:34 PM
On select dates, the French Lick Scenic Railway adds a social twist with its popular Beer Tasting Train—a 21+ evening built around craft pours, rail ambience, and views you can’t get from the highway. -
Wisconsin ~ Wild West ~ Train Rides
Jul 14, 26 12:10 PM
Through a unique blend of interactive entertainment and historical reverence, Wisconsin offers a captivating glimpse into the past with its Wild West train rides. -
Georgia ~ Wild West ~ Train Rides
Jul 14, 26 11:46 AM
Nestled within its lush hills and historic towns, the Peach State offers unforgettable train rides that channel the spirit of the Wild West. -
Florida ~ Wine Tasting ~ Train Rides
Jul 14, 26 11:34 AM
Wine by train not only showcases the beauty of Florida's lesser-known regions but also celebrate the growing importance of local wineries and vineyards. -
Texas ~ Wine Tasting ~ Train Rides
Jul 14, 26 10:05 AM
This article invites you on a metaphorical journey through some of these unique wine tasting train experiences in Texas. -
New Mexico ~ Wine Tasting ~Train Rides
Jul 14, 26 09:26 AM
For oenophiles and adventure seekers alike, wine tasting train rides in New Mexico provide a unique opportunity to explore the region's vineyards in comfort and style. -
Tennessee ~ Murder Mystery ~ Dinner Train Rides
Jul 14, 26 09:10 AM
Amidst the rolling hills and scenic landscapes of Tennessee, an exhilarating and interactive experience awaits those with a taste for mystery and intrigue. -
California ~ Murder Mystery ~ Dinner Train Rides
Jul 14, 26 09:01 AM
When it comes to experiencing the allure of crime-solving sprinkled with delicious dining, California's murder mystery dinner train rides have carved a niche for themselves among both locals and touri… -
North Carolina ~ Wild West ~ Train Rides
Jul 13, 26 01:49 PM
North Carolina, a state known for its diverse landscapes ranging from serene beaches to majestic mountains, offers a unique blend of history and adventure through its Wild West train rides. -
Pennsylvania ~ Wild West ~ Train Rides
Jul 13, 26 01:45 PM
The Keystone State is home to a variety of historical attractions, but few experiences can rival the excitement and nostalgia of a Wild West train ride. -
New York ~ Wine Tasting ~ Train Rides
Jul 13, 26 01:40 PM
This article will delve into the history, offerings, and appeal of wine tasting trains in New York, guiding you through a unique experience that combines the romance of the rails with the sophisticati… -
Michigan ~ Wine Tasting ~ Train Rides
Jul 13, 26 01:35 PM
In this article, we’ll delve into the world of Michigan’s wine tasting train experiences that cater to both wine connoisseurs and railway aficionados. -
Illinois ~ Murder Mystery ~ Dinner Train Rides
Jul 13, 26 01:32 PM
Among Illinois's scenic train rides, one of the most unique and captivating experiences is the murder mystery excursion. -
Vermont ~ Murder Mystery ~ Dinner Train Rides
Jul 13, 26 01:28 PM
There are currently murder mystery dinner trains offered in Vermont but until recently the Champlain Valley Dinner Train offered such a trip! -
The Flying Scotsman’s American Adventure: LNER 4472’s U.S. Tour
Jul 13, 26 12:02 PM
In the fall of 1969, a gleaming British steam locomotive unlike anything most Americans had ever seen rolled into Boston and spent the next four years touring the U.S. -
Amtrak's California Zephyr – Complete Scenic Route Guide 2026
Jul 12, 26 01:04 PM
Explore Amtrak’s California Zephyr, one of America’s most scenic long-distance train routes. Complete 2026 guide with highlights, best times to ride, what to expect, photography tips, and fall foliage… -
Alabama ~ Wild West ~ Train Rides
Jul 12, 26 12:25 PM
Although Alabama isn't the traditional setting for Wild West tales, the state provides its own flavor of historic rail adventures that draw enthusiasts year-round. -
Indiana ~ Wine Tasting ~ Train Rides
Jul 12, 26 12:22 PM
In this article, we'll delve into the experience of wine tasting trains in Indiana, exploring their routes, services, and the rising popularity of this unique adventure. -
South Dakota ~ Wine Tasting ~ Train Rides
Jul 12, 26 12:04 PM
For wine enthusiasts and adventurers alike, South Dakota introduces a novel way to experience its local viticulture: wine tasting aboard the Black Hills Central Railroad. -
New Mexico ~ Murder Mystery ~ Train Rides
Jul 12, 26 11:41 AM
Among Sky Railway's most theatrical offerings is “A Murder Mystery,” a 2–2.5 hour immersive production that drops passengers into a stylized whodunit on the rails. -
Michigan ~ Murder Mystery ~ Dinner Train Rides
Jul 12, 26 11:36 AM
Among the lesser-known treasures of this state are the intriguing murder mystery dinner train rides—a perfect blend of suspense, dining, and scenic exploration. -
Best Christmas and Holiday Train Rides in the Eastern U.S. 2026
Jul 12, 26 11:05 AM
Discover the best Christmas and holiday train rides in the Eastern U.S. for 2026, including Polar Express experiences, Santa trains, and festive scenic journeys. Plan your magical rail adventure this… -
New York ~ Wild West ~ Train Rides
Jul 12, 26 09:53 AM
Join us as we explore wild west train rides in New York, bringing history to life and offering a memorable escape to another era. -
Ohio ~ Wild West ~ Train Rides
Jul 12, 26 09:38 AM
For those enamored with tales of the Old West, Ohio's railroad experiences offer a unique blend of history, adventure, and natural beauty. -
Western Pacific's 4-6-6-4 "Challengers" (M-100)
Jul 11, 26 11:29 PM
In the late 1930s, the Western Pacific stood at a crossroads. Traffic volumes were recovering from the Great Depression, and the railroad needed more powerful, faster locomotives to move longer freigh… -
Cass Scenic Railroad Fall Foliage Trips 2026 – Complete Guide
Jul 11, 26 04:28 PM
Plan your 2026 fall foliage trip on the Cass Scenic Railroad. Complete guide to the Bald Knob route, schedules, what to expect, photography tips, and why this West Virginia steam train ride is one of… -
Best Fall Foliage Scenic Train Rides in the Eastern United States 2026
Jul 11, 26 03:16 PM
Discover the best fall foliage train rides in the Eastern U.S. for 2026. From steam-powered mountain climbs in West Virginia to scenic heritage railroads across the Appalachians and beyond — plan your… -
Missouri ~ Wild West ~ Train Rides
Jul 11, 26 11:27 AM
In Missouri, a state rich in history and natural beauty, you can experience the thrill of a bygone era through the scenic and immersive Wild West train rides. -
Indiana ~ Wild West ~ Train Rides
Jul 11, 26 11:17 AM
Indiana offers a unique opportunity to experience the thrill of the Wild West through its captivating train rides. -
North Carolina ~ Whiskey Tasting ~ Train Rides
Jul 11, 26 11:05 AM
One of the GSMR's most distinctive special events is Spirits on the Rail, a bourbon-focused dining experience built around curated drinks and a chef-prepared multi-course meal. -
West Virginia ~ Wine Tasting ~ Train Rides
Jul 11, 26 10:45 AM
West Virginia, often celebrated for its breathtaking landscapes and rich history, offers visitors a unique way to explore its rolling hills and picturesque vineyards: wine tasting trains. -
Utah ~ Wine Tasting ~ Train Rides
Jul 11, 26 10:42 AM
Utah, a state widely celebrated for its breathtaking natural beauty and dramatic landscapes, is also gaining recognition for an unexpected yet delightful experience: wine tasting trains. -
Virginia ~ Murder Mystery ~ Dinner Train Rides
Jul 11, 26 10:12 AM
Among the state's railroad attractions, murder mystery dinner trains stand out as a captivating fusion of theatrical entertainment, fine dining, and scenic travel. -
Maryland ~ Murder Mystery ~ Dinner Train Rides
Jul 11, 26 10:02 AM
Maryland is known for its scenic landscapes, historical landmarks, and vibrant culture, but did you know that it’s also home to some of the most thrilling murder mystery dinner trains? -
U.S. Rail Traffic Surges 8.7% in Holiday Week Ending July 4, 2026
Jul 10, 26 03:39 PM
Despite the Independence Day holiday (which fell on a Saturday), U.S. freight railroads delivered an impressive performance, posting an 8.7% year-over-year increase in total traffic -
APSL Nears Acquisition Of B&O Depot In Paw Paw, WV
Jul 10, 26 11:44 AM
After decades of quiet abandonment, a dedicated preservation effort by the Allegany Preservation Society Limited (APSL) is racing to secure its future— having already raised approximately 90 percent o… -
Minnesota ~ Murder Mystery ~ Dinner Train Rides
Jul 10, 26 10:05 AM
Murder mystery dinner trains offer an enticing blend of suspense, culinary delight, and perpetual motion, where passengers become both detectives and dining companions on an unforgettable journey.
