Software migrations are never easy, rarely go 100% as expected, and are always “fun”. But what if we scaled up the stakes and migrated an entire country?

Pete Cheslock used Swedish historical examples to compare “17th Century Shipbuild and Your Failed Software Project” (a must-watch, by the way). Picking on Sweden further, let’s reflect on how they approached migrations.

Swedish Calendar

In 1699, Sweden decided to gradually transition to the Gregorian calendar, which was already widely adopted in Europe. The migration was to take 40 years, skipping all leap days between 1700 and 1740, thereby getting one day closer to the Gregorian calendar every four years.

However, after the first leap day omission in 1700, further changes were halted due to the outbreak of the Great Northern War.

In January 1711, Sweden decided to revert to the older Julian calendar, creating the rare, if not unique, 30th of February historical event.

Finally, in 1753, Sweden switched to the Gregorian calendar in one leap.

Some other countries also considered a prolonged migration but ultimately decided on a single-step change. That’s how Belgium and the Netherlands skipped their Christmas, jumping from December 21st to January 1st in 1583.

This may already feel familiar

  • Increased risks of prolonged migrations
  • Priorities and requirements changing mid-way
  • Unhappy voices before, during, and after the migration
  • Costly reverts
  • Unexpected failures in the process

Dagen H, aka Högertrafikomläggningen

Lesson learned, in 1967 Swedes had a much smoother transition from driving on the left to driving on the right side of the road, making a change within a single day, the day “H”.

How did they do it? By printing the event logo on panties and milk packaging!

Kungsgatan, Stockholm at the transition from the left to right-hand traffic, 3 September 1967, at. 4:50 in the morning.
Kungsgatan, Stockholm on 3 September 1967, at. 4:50 in the morning.

Jokes aside, several factors contributed to a successful, uneventful migration

  • Understanding the need:
    • Standardization: All neighboring countries drove on the right
    • Access to cheaper resources: Wider variety and lower prices for left-hand-drive cars.
    • Actual readiness for change: Over 90% of cars on the road were already left-hand.
    • Safety concerns: Accidents from head-on collisions when passing with left-hand-drive cars on narrow highways.
  • Running cost analysis:
    • Future costs: The number of cars on the road was expected to increase from 0.5 million in 1963 to 1.5 million in 1967 and up to 2.8 million by 1975.
    • Increased cost burden on vehicle owners: For example, right-side-driving headlight replacement as the trend moved towards more expensive model-specific lights instead of standard round lights.
  • Proper planning and preparation:
    • 4 years of nationwide preparations.
    • Extensive advertising.
    • Nationwide road marking, traffic sign, and signal preparation.
    • Consulting psychologists and preparing an education program.
  • Asking for forgiveness vs permission:
    • A prior 1955 referendum had 83% of votes against the change.
  • Execution:
    • All hands on deck: road workers, police, helpers, etc.
    • Larger cities had longer blackouts to allow road workers to reconfigure intersections.
    • 1am - 6am, all non-essential traffic was banned from the road
    • 4:50am every vehicle had co come to complete stop, change the side of the road, stop again, and wait for others to complete.
    • 5:00am vehicles were allowed to proceed

Historical footage of the event is available for those interested.