This study evaluated the vehicular speed reduction effects of displaying speed limit and information messages on a changeable message sign (CMS) placed inside the work activity area in a work zone for a one lane closure on a rural interstate highway. It also examined the additional effects of using two CMS devices compared to one CMS. The following three experiments were conducted: (1) One CMS in advance of the work zone (Experiment 1), (2) One CMS inside the work activity area (Experiment 2), and (3) Two CMSs inside the work activity area (Experiment 3). Displaying speed limit and information messages on CMSs placed in the work activity area was effective in reducing the average speed and percentages of vehicles with excessive speeds. Comparing the results from Experiments 2 and 3 indicated that displaying the CMS messages reduced the speed of cars immediately after passing the CMS, but not at a point far from the CMS. Although trucks did not consistently reduce their speeds near the first CMS, trucks traveled at reduced speeds after passing the CMS. Cars and trucks reduced their speeds by as much as 5 and 4 mph, respectively, near the CMS. The speed reduction depended on the travel speed of the vehicles. Placing the CMS in the work activity area was more effective than putting it in advance of the work zone.