Washington: US authorities are ramping up security measures for the long Independence Day holiday weekend in the wake of deadly terrorist attack at Istanbul airport. Washington is always a popular July 4 tourist destination, attracting tens of thousands of visitors, Efe news reported. The city government has announced the deployment of additional uniformed police around malls, financial institutions, houses of worship, hotels and other places where large numbers of people congregate. The police department is also putting more plainclothes officers on the street, along with bomb-sniffing dogs and radiation-detection units. Most of the roughly 43 million people expected to be travelling during the course of the three-day weekend will be on the highways, but an estimated 3.3 million are projected to pass through the nation's airports. This year has already seen an increase in the time needed to get through security checkpoints at airports, attributed to personnel shortages at the Transportation Security Administration. Southwest Airlines advised passengers to arrive at the airport two hours ahead of the scheduled departure for domestic flights and three hours for international flights.