The dimensions of the bridge are 24.9 feet in length (of the largest span), but a total of 73.2 feet with a deck width of 37.1 feet. There is a engineering landmark plaque on the northern side of the bridge. It is graffitied of course but I photoshopped it to show its original look.
From Wikipedia
The Frankford Avenue Bridge, also known as the Pennypack Creek Bridge, the Holmesburg Bridge, and the King's Highway Bridge, erected in 1697 or 1698 in the Holmesburg section of Northeast Philadelphia, Pennsylvania, is the oldest surviving roadway bridge in the United States.
The bridge, built at the request of William Penn, was an important link on the King's Highway that linked Philadelphia with cities to the north (Trenton, New York, and Boston). Over it crossed anyone who traveled by horseback or coach from the northern colonies to the First or Second Continental Congresses, such as John Adams, from Massachusetts. In 1803, it was paved, and a toll booth was added at its south end. The bridge was widened in 1893 to accommodate streetcars. It remains in use today. The bridge was designated a National Historic Civil Engineering Landmark by the American Society of Civil Engineers in 1970. It was listed in the National Register of Historic Places in 1988.
I found an excellent website which tells more about this bridge:
Pennypack Bridge-Kings Highway. The bridge was erected in 1697 and is the oldest stone arch bridge in continous use in the United States. The road it carries over the Pennypack has changed from a path to a toll road to a modem city street. The name changed from King’s Path, to King’s Highway, to Bristol Turnpike, to Frankford Road, to Frankford Avenue (US #13). Prior to the construction of Roosevelt Boulevard (U.S. #1) in the 1920s, the road was the main route from Philadelphia to Trenton, New York, and points north.
Over the bridge have come the Lenni-Lenape, the Continental Army, members of the first Continental Congress, farmers on their way to the Mills along the Pennypack, and the common traveler. The Massachusetts delegation, including John Adams, dined at the Red Lion Inn at the Poquessing, on August 29, 1773 and then crossed the bridge on their way to Philadelphia. Washington passed over the bridge and stayed at the Inn at the south side of the bridge which later became the Washington Inn during the Revolution. He passed over the bridge ceremoniously on April 30, 1789 on the way to New York, for his first Inauguration.
The Pennypack Bridge became the center of controversy as the road became burdened with more and more traffic. On March 24, 1803, the Frankford and Bristol Turnpike Company was formed. The old road became a macadam road. A toll house was placed at the south end of the bridge, north of the Mill Race. The toll gate was in operation until July 1, 1892 when that portion of the turnpike was sold to the City of Philadelphia.
The first trolley went into service over the bridge from Cedar Hill (Frankford Avenue and Bridge Street) to the Poquessing in 1895. To accommodate the increased traffic the bridge was widened and heightened in the late 1890s and early 1900s, but it kept the original style. In 1928 there was a call to demolish the bridge and replace it with a wider one was quelled. The bridge still stands today. SOURCE