In the wee hours of this morning, most of the United States moved to Daylight Savings Time (DST).
For a number of years, DST began the first Sunday in April. This year, Congress approved an earlier start date for DST - the second Sunday in March. The rationale for this was that the extended daylight in the early evening would reduce energy costs and improve automobile safety.
For a majority of Americans, the change will likely have precisely that effect. Morning commutes and other routines will not be greatly affected, but evening commutes and routines will be enhanced by the extended daylight hours.
However, for a portion of the country, the change may not have a completely positive net effect on energy and safety. Those are the parts of the country that are located in the eastern portions of their time zones.
Time zones were originally created in the nineteenth century to provide some uniformity to railroad schedules. They were grounded in the system of longitude based at Greenwich, England. As there are 360 degrees of longitude in total, and 24 hours in the day, each time zone would encompass about 15 degrees of longitude. The time zones would be centered - roughly - on the longitudes evenly divisible by 15; in the United States, these "center meridians" would be 75, 90, 105, and 120 degrees west of Greenwich.
As time zones actually evolved in the United States, and population grew, the effective centers of the time zones moved west. Only 11 states - with less than 20 percent of the nation's population - are either mostly or entirely east of the "center meridians": the six states of New England, New Jersey, Illinois, Wisconsin, Alabama, and Nevada. In these places, the sun rises and sets earlier than in the rest of their time zones.
The effect of the earlier switch to DST in these states is that the early morning, which had been seeing daylight, will go dark again for another month. In Boston, the sun rose yesterday, at 6:08 AM EST. Today, it rose at 7:06 AM EDT. In Chicago, the sun rose yesterday at 6:14 AM CST. Today, it rose at 7:12 AM CDT.
In metropolitan areas like Boston and Chicago, there are many people who rise early and arrive home late. The later sunrise might actually mean increased energy use for such people. It will be interesting to see the effect on energy usage in such places.